Thanks for interesting video. The latest inverter driven preheated scroll compressors are far less adversely affected by cycling than old tech reciprocating compressors. Also for latest heat pump models such as the Mitsubishi Ecodan R32, during periods of mild ambient temps and low heat demand, the auto adaptive management software prevents cycling by running at no less than minimum continuous power, allowing roomstat temp to overrun target temp by one degree of headroom, then switching off for however many hours are required for roomstat to cool back down by that one degree to target room temp, then the heat pump restarts again, and so on. Even for an oversized heat pump this avoids cycling altogether, so has no impact on efficiency. I have an oversized heat pump, being an 11.2kW model compared to design spec. recommendation of 8.5kW, but my performance stats are at least as good as manufacturer's data table specs. Also the 11.2kW is more efficient at exceptionally cold, high heat loads where the extra headroom is essential.
The issue of maintaining a high flow rate for heat pump efficiency seems to come up a lot in discussion groups, whether that’s expressed as pros and cons of buffers, zoning, or TRVs.
John Cantor: Thank you. I am just having my second winter with a heat pump and it is working pretty well - SCOP last winter was 3.6. However I have a feeling it could work better. Once the external temperature rises above ~ 5 °C the heat output falls below ~ 2 kW - and the system cycles. This is ~ 40% of the nominal maximum output of a 5kW Vaillant Arotherm Plus pump, and like you said, I think that's just a choice by the manufacturer to set the lowest output at about 40% of maximum. Understanding of what is going on is compounded by a complete lack of 'User Manuals', but I have concluded it is probably just not worth worrying about. All the best Michael
@@hvacdesignsolutions Hi. That's possible. I do have a Low Loss Header, and I have been experimenting with changing the power of the pump which re-circulates water from the Low Loss Header through the radiators. At current temperatures,(
Thank q very much for putting this video together very informative , I have recently had a quote for a 9 kw heat pump which I thought was two big ( I used actual heating usage data rather than calculated ) and got the size to 5-6 kw but this helps me a lot
I'm in the exact same situation. My WORST scenario in actual heating usage (calculatede on 6 years bills) is 4,5Kw, they quote a 8Kw heat pump that give 7,28 Kw @ -7/35 ... and my external project temperature is -5 so .... WHY???
@hardcard254 thanks. Re your flow rate, have you considered adding a pump in-line? So long as the extra pump is on a fixed speed setting, you should be ok. I have had 2 pumps in series on few occasions. The WiloPico with the green knob (not red) is great since the display shows watts, flowrate and also pressure.... Ideal for setting it up, and much easier than replacing pipework!
It's interesting to hear you mention a buffer tank @ 16:55, for the larger 16kW unit. Most installers I speak to, don't put them in. I wonder if thats because of the additional cost to the homeowner, or the installer doesn't understand how and when a Buffer Tank should be applied..........maybe something to consider for your next video.
Very interesting. 'Good cycling'' seems to be nothing to be worried about, notwithstanding start/stop wear on the compressor, however it should be remembered that fridges and freezers happily cycle throughout their lives and last an awful long time (generally they are retired for other reasons!)
Late to the party, per usual🤔 What came to mind during this presentation, and thank you for your efforts and the knowledge you have provided; however, I was wondering if instead of heating the water that would flow through the system (pick your preference) would it make sense to have a large enough buffer tank(s) to provide the heated fluid and have the heat pump spend a longer period just bringing the buffer tank(s) back to their setpoint? If possible, would it make sense to design/install a system with a lead-lag buffer system for use?
Well... buffer tanks have been used in the way you describe for a long time. If space is available, yes, they can be a good idea. There are however a few down sides. Often, the average water temperature that the heat pump 'sees' is a few degrees higher than the emitters actually get. This rise tends to reduces to COP. Also, if the buffer is going to store any amount, it may need to rise several degrees above what is needed... e.g. a 200litres (typical size) tank , with 10kW heat input, would rise 10c (18F) in only 14 minutes, (using heatpumps.co.uk/calculators/ ) So buffer tanks need to be quite big if they are going to store a wothwhile abount. They also add a considerable expense and complexity. It may be worth it in some cases. Again, the majority of houses would probably prefer not to loose the space required for the tank.
Thank you - I think you've answered one of the questions that I had in mind - over-sizing is well known but under-sizing not so much it seems - what I was trying to understand is at which point in modulation the efficiency is highest and the EcoForest graphs seem to answer that - my thinking is that heat loss sizing is done for a -3C outdoor temp but actually in reality that only happens for a handful of days in the UK, which essentially means that the HP will not need to deliver as much heat on an 'average day' and thus be in the very low region of modulation, which could result in inefficiency and cycling too - so ideally, assuming the OEM has it programmed to not hit the very low modulation levels, the sweet spot for heat output versus heat loss is somewhere in the middle on an average day - or am I barking up the wrong tree? For very cold days, it may run at fullish output for longish periods rather than being scaled so that it only needs to run there at start up or on very cold days?
Mmm.. well, whilst that Ecoforest graph is interesting, maybe it could also be a bit misleading here since there are other factors (like water temperature) that are probably more important. e.g. whilst a 'small' unit might run at high revs a lot mid winter, it should also spend a lot of hours at mid speed, and it could probably run at lower temperature (less rest time). A big unit is likely to 'stray' into higher flow temperatures at times, and may spend a lot of the year cycling. How it's operated also has a bearing on things. e.g. if its fairly constant, or if it has long-ish rest times. Finding the best efficiency relating to unit size (wrt heat demand) seems hard to assess, and no doubt its the extremes that are the worry, and a region in the middle with similar performance. I think you are barking up a similar tree. Maybe theory and practice don't quite match since heating a house is a dynamic thing... (day/night), and all buildings and occupants are a bit different. Not sure if that helps!
@@johncantor4056 thanks yes that is helpful - as you say it's not clear cut and I was sort of comparing it to very "1 dimensional" controls on a gas boiler without weather compensation so hadn't considered water temperature aside from the assumption that if an "average" property has an 'over-size' condensing gas boiler, it can be dialled down to reduce the overall output, provided the rads can emit the heat, then it can happily output constantly at its lowest modulation, but if like one of the examples you showed, where little else was done and a 'like-for-like' HP replaces a gas boiler, it would be better to go smaller instead, but would that have a detrimental impact on the efficiency? I guess inverting HPs have a wider working range and so as you say avoiding those extremes is the key. Plus if done as a retro-fit without other changes like bigger rads and more insulation, those things can be done afterwards and thus erring on the smaller side would still be a better bet than worrying about those few days where the 'calculated' heat losses at -3C make people think they need to 'go large' in order not to feel cold...on those days, a smaller HP could easily just run continuously in a more efficient manner rather than the on/off manner of heating that so many people are used to in this country!
Surely the cop is very poor on a cold start before the compressor becomes warm and smooth ? One graph at 1355 shows a huge rise on a cold start ? Great video, thanks
You are right that COP at start (after a long rest) is poor as it warms everything up. Compressor would be warm though if starting when cycling is frequent. There is however another thing at play... at start-up, the compressor pressures are equal, so the compressor has a very 'easy ride' at first, until the pressure difference across the compressor builds up, so at start, if it were not for various inefficienies, the COP would be much higher at start up
Thank you for this wonderful information and clear presentation. My system is a ducted Mitsubishi variable speed 36k BTU heat pump in Seattle WA USA where our cold temps are generally near 32 deg F but recently we had a week of 16 deg. 2700 sq ft house. Given the goals of minimizing cycling and having our variable speed heat pumps run continuously at low flow temps; If we like it cool at night can we turn the thermostat down in evening and then just heat very gradually in the morning by turning thermostat up 2 degrees at a time over couple of hours? Does the heat pump measure the outside temperature and work harder / increase the flow temperature when it’s very cold outside? I notice air temps from my vents vary from 80-100 deg. Does the heat pump work harder if thermostat set 10 deg over current room temp compared to only a set point of 2 deg higher; and does this harder work make the air flow temps higher? Thank you for your generous work and presentation
Thanks for your comments.. I wish I could answer your question, but I dont actually know how the air-air control works. I would expect the system to register how many degrees the actual room temperature varies from the set-point , and respond accordingly... surely that is how it must work. i.e. as the room setpoint is approached, the compressor slows down, along with the fan speed. this gives the best comfoort. But does it also vary with respect to the outside temperature? I would expect it does. Given that a heat pump could give out twice the heat in mild weather compared to what it can give out in cold weather, then some sort of limitation for mild weather is surely part of the strategy. I would be interested to know.
Thanks, I think you’re right. Outside temp and temp differential (outside to set point) should be what the computer is most interested in. The heat pump must work harder if outside temp is cold and if your set point is a large jump up from current room temp; hence my theory of inching my thermostat up a couple degrees at a time as room gradually warms. Hopefully keeps compressor work light and air flow temp lower. My rough estimate is my heat pump electricity consumption goes up about 3% for every degree I turn up the thermostat and also goes up 3-4% for every degree the outside temperature goes down. Either way it makes sense as I’m increasing the differential from outside temp to thermostat set point. My electricity use was doubled with our recent week of 16 deg temp. House is old, could use better insulation, and Seattle homes not built for that. Thanks again for interesting discussion Steve
@@yt551217 In colder weather, the compressor will need to spin faster to get the same heat output, and in cold weather, more heat is needed, so surely it manages this intelligently in some way. Sounds like you are doing the right thing by increasing it slowly
You mention in this video at one point that maintaining the room temp slightly below the set point is ok. Is this just for a heat pump which can run continuous at low temps to balance the heat loss of the room/building? I have a gas boiler that I am running at low flow temps to determine if my property is "heat pump ready". I have been frustrated this winter that the set point is not being achieved but instead remains usually within 0.5 degs and the boiler cycles most of the day sort of balancing the heat loss of the room. I am probably being stubborn as I know the main living area has undersized radiators for low flow temps so this should be expected. I have smart controls so I am mostly disappointed the control cannot adapt and run the boiler for longer but due to smart TRVs I think this may be a limit of the system not having enough emitters at times and overheating rather than the controller.
I think I am getting at point that its generally better to keep the heat pump running in cold weather, so you dont really want the room thermosts turning it off... e.g. lets say it's running very happpily and steadily in cold weather (though might be interrupted by defrosts every say 40 mins). Anyhow, if the thermost turns it off, then there can be some catching up to do which may not be easy. Ideally the compressor will modulate down and keep running. The manufacturers thermosts is usually best, and this is where 'room target' or 'auto adapt' can work very well. In your case, I guess you are trying to vary/reduce the water temperure to see if say 40C is enough etc. Maybe your smart stats are trying to be too helpfull! can you simply turn the TRVs to max for your experiments?
Interesting video. COP while important I think is often over emphasised. COP I believe is analogous to a cars MPG, and what home owners really need to know is an equivalent to cost per mile - which changes with everyone's use case. Sticking with the car analogue- Getting a diesel with the best maximum potential MPG may not be the cheapest per mile option in the real world for someone who has to do lots of short journeys.
Yes I agree that COP is sometimes used too much (given too much 'weight'). Its actual energy use that's important. But lets say you improve all journey types by correct tyre pressures, then all MPGs might improve by say 10% for all... But, skewed as you say because diesels are not so good at short journeys. Its a matter of testing in relevant condition.
Excellent stuff !! I am planing to have an Ashp installed, but not decided yet if Daikin or Panasonic. Nevertheless, I plan to have also a 200 liter buffer installed (for defrosting and to reduce on/offs). My question would be how the buffer should be installed? In series or in parralel ? Thanks!
Thanks Adrian. I suggest your first enquiry about configuration should be with the manufacturer. They will have worked through buffer options, and how it relates to their particular controls and they will have sensor positions in mind. I have seen a few very bad buffer tanks where a lot of unwanted mixing happens inside them, so there are pitfalls to avoid. e.g. where to get 35C at your radiators, you need 40C at the heat pump. In this case, dropping the COP considerably. If it's only system volume for defrost that is the worry, then a small 2-pipe volumiser seems a good idea to me. I have never understood why manufacturers don't start defrost in the normal way, and if there isnt enough heat in the radiator circuit, it briefly diverts to DHW. This should 'steal' only a tiny bit of DHW heat, and only in certain conditions. Anyhow, each heat pump has different requirements, so you need to refer to the manufacturers recommendations.
Hi John, Thanks for this informative video. I have an LG Therma V Monobloc R32 9kw heatpump and I see it cycles time to time working for about 30-40 mins and waiting for another 5-10 mins and cycling again. I understand that it's not a problem, but still struggling to understand why it overshoots the target temperature but instead not gradually slowing down while reaching the target temperatures. Should I be worried? (I have a 300lt DWH tank and 100lt buffer tank, radiators are connected to this buffer tank with a cycling pump and my tado is controlling this cycling pump, not controlling the Heatpump)
Hello. I'm wondering if this 'cycling' is actually defrosting. This can happen about as you describe, and will a lot in cold damp conditions. Actually worse when say 0C to +5C. Nothing to worry about. If you catch it stopping, you should see the white frost on the fins melt over a few minutes. Otherwise, in this weather, the unit is likely to run steadily. They generally vary (modulate) between 33% and 100%. When the heat demand is lower, (milder weather) it will need to cycle, and cycling on/off mid range can sometimes be better than running steadily at 33%. difference between the two is often slight.
John, very interesting, though I am an engineer and try to make sense of my 7kw Vaillant heat pump, if I show you my Ubibot flow temp-in at the buffer tank for a week, would you be able to comment? not sure if you have an email I can send the data to? myVaillant app is showing a SCOP between 4-4.5 with my heat curve set at 0.8 and max flow temp at 45 and min at 25degC, would like to know if you can see the suggested back in the amount of cycling my heatpump does? cheers Mark
I'm curious what the difference there would be with longer cycle times - Ecodan controls have a setting of 10-60 mins which I assume is a forced off period (doesn't seem clear in manual) - I'd hope you'd minimise those refrigerant start up losses and see some benefit of the low system temperatures on restart with longer off periods and hence (hopefully) longer on periods?
Yes, its not clear in Ecodan info, but I think the 10-60 is related to time response of room sensor. I guess some 1/2hr rests should result in some better COP due to cold start, BUT it will 'rev up'. Shame there is not an 'economy' setting, maybe watching outside temperature, that would stop it going to maximum speed so eagerly.
@@zlmdragon. I have never quite understood this setting. There seem to be other factors at play. Of course the actual compressor speed is all important, and I found the 6kW 'revs up' unnecessarily even when its quite mild out. I expect some 'rev ups' are there to help compressor lubrication, but I still find it straying to high output, unlike the older models. I guess there are 2 main considerations a) ensure that enough heat is being delivered, b) minimise running cost. It seems to be programmed mainly for 'a'
Hi John I have a heat pump which is oversized I believe our heat pump daikin atherma 3 is 9kw and our design temp is 5kw @-2. The heat pump will module to about 30% I am told but this would still be too high in the spring/auturm months. Would a buffer help with the efficiency? We currently have a 25litre but was thinking of upping it to a 90L based on a calculation I got off google. This is piped as a LLH with a secondary circulation pump. Any help would be greatly appreciated.
Hello Roman. You can look at my calculator at heatpumps.co.uk/calculators/ to help assess buffer sizes. It might be useful. It's not that straightforward because lets say your 9kW Daikin actually only drops to say 4kW in milder condition, and all is in steady-state and happy, then if you need to cycle, as the radiators rise above the temperature you need, then unfortunately, it wont re-start at 4kW again. Instead, it will 'rev-up' a bit, possibly to 9kW for a short while before it slows down again. (I actually don't have much experience with Daikin) So, to be clear, the buffer volume will slow down the rate of water temperure rise, so it should help, but there are more than one way to configure a buffer tank, of which small details like the sensor positions is important. You are adding complexity. I suggest you go with Daikin's recommendations because they will have developed their controls to work in a certain way.
Unless you have ground heating or a large / complex installation, it's likely that you don't actually need any buffer tanks or secondary pumps. Find out whether your installation meets the water volume requirement for your HP on its own, without the 25 litre buffer tank... if it does, get rid of it and get rid of that secondary pump too. Your COP is likely to improve.
Hi John, Thanks for your videos, I have a 10 year old Daikin ASHP and I would like to monitor it more closely, its doesn't have any interface to allow me to see what its is doing. I notice that the openenergy monitor uses heat meters to measure the flow and returns temperatures, I would love to do that but those devices are very expensive. Is it possible to do something similar using DS18B20 sensors (or similar) taped to the main flow and return and use these to estimate the energy? I have a feeling that there is good reason why this would not work but I would like to know if there is a cheaper way of adding some better monitoring to my ASHP. Thanks
Yes, heat meters too expensive for most people. I think a lot can be gleaned from sensors on pipes. The heat (kW) is proportional to flow-return dt. IF flowrate constant. e.g. if you look at my graph at 2:40 in, and measure (with a rule) the dt at 27C point and 29.5C point, I make it 16mm and 15.5mm.. so the dt has reduced a tiny bit, but input power has increased, so COP a bit worse. This is just an example of what you might be able to glean. However, if water flow changes, this is meaningless, so you need to do specific experiments, and repeat a few times.
@@timcx I’ve got a hitachi yutaki I’m trying to get to grips with in terms of flows and cycling. It doesn’t have good data output either, I’ve recently found home assistant and Shelly iot devices. You need a bit of IT skills but you can get a lot of info from Shelly em and some temp sensors.
@@simoncanfer5030 Hi Simon how are you collecting the temperatures, what equipment are you using? I was thinking of using EmonTx but open to other ideas.
There are too many dts! If the flow-return dt is large, then the condensing temperure is likely to be closer to the flow temperure, BUT the system is worse off because the mean temperature to the heating system is worse... I think this needs spelling out with a sketch... thanks for highlighting it. The COP estimator is fairly simple. I tried to make a version to include flow-return dts, but it became unnecessarily complicated!
@@johncantor4056 Yeah, with lower flow rate dt we can get higher medium temperature and it means that we can use lower LWT. But on other side if lets say we apply dt = 5 for cold weather, than for moderate weather dt can be 2 or even 3 and heat pump can start cycling. I am just playing with configs of my heating system and trying to get the best SCOP. My heat pump can't work constant with dt < 3.5(that's for moderate weather that I have 90% of time). In this case LWT starts to raise as heat pump starts to increase frequency. And it can just work with higher LWT(1-2 higher than needed) or starts to cycling. Can't find any info if it happens due to algo on my heat pump, or it's physical limitation of process that happens inside condenser. Maybe if dt is too low, gas can't transfer to liquid on 100% and that's why heat pump starts to increase output (some kind of protection). For now seems I need to make dt 4-5 for moderate weather and 8-10 for really cold weather. Or make a variable flow rate.
Maybe it's also the limitation of compressor speed that you mentioned in the video. I see that it avoids to work with frequency less than 35-40% and power consumption less than 20% of max.
The estimator assumes a certain flow temperature, and if the flow-return dt changes, (assuming same heat (kW), then the flowrate must be changing, and return temperature is changing too. An alternative would have been to give a 'mean' flow-return temperature, and this might be more relevant to water-to-refrigerant dt. I somehow need to spell this out better because as it stands, it looks like you can change the 'offset' and change the COP, however, the 'offset' is more a function of heat-exchanger size/compressor speed than anything else. I am pondering it.
Its a bit complicated since many systems have a fixed flow circ pump, so typically, if flow-return dt is 5 at high power, then it will naturally become 2.5 when the system is 1/2 power. Other systems simply 'track' the flow and return temperatures, and they adjust the circ pump automatically so the flow-return dt stays at 5 degrees (kelvin/Celsius). Furthermore, some systems might assume a fixed flow, and the control uses the dt value as control in some way. That might seem all a bit daunting, but I dont think fine-tuning of dt will actually affect the COP much. However, if the dt is 6 or more then the return is getting cold, so the flow temperure may need to be warmer to compensate, so for that reason, a large dt is rarely desirable.
There’s a lot to digest in your video. Thanks for posting it. Here’s a video where I examine the performance of my own heatpump: th-cam.com/video/QAKLrVAdvQ0/w-d-xo.htmlsi=H3oZ9isini3LlF93 I came to different conclusions as to why my COP was getting worse for higher ambient temperatures, but since that video I’ve gotten even newer insights into my heatpump performance. What I’m seeing is that flow return delta T is shrinking from 4 degrees to 1-2 degrees during milder weather and warmer room temps leading to bad COP. But when the house is warming up from cold following a vacation, the COP is much higher. So I’m wandering if actually my radiator TRVs are the culprit, despite being on the maximum end stops. I’m wandering if they are closing in anyway
Hello Anthony.. i look forward to watching your video through ( no time right now!!).. One initial question.. how accurate do you think your heat assessment is when dt is less than 2? A small sensor error will make a big difference. with no heat, bit pump running, what dt is showing on the heat meter? Is it zero? I will watch your video soon,
@@johncantor4056 Hello John I find the flow sensor minimum reading is 6.5l/min (which is also what the manual says) and the next lowest reading is 7.1l/min so that’s just over 10% error. Likewise when it comes to the primary current reading for the compressor the lowest readings are 0.5, 1.3, 1.8, 2.3 Amps etc… There’s absolutely no variation in between those discrete readings. What this means is very choppy current and flowrates and therefore very choppy instantaneous coefficients of performance. However when you average it out over the course of 10 minutes then you get some quite revealing trends happening, I tend to use 10 minute averages to determine what’s going on with my heat pump. DeltaT temperatures are accurate to within 0.1 degrees on both the flow and return temperatures. I am able to determine the accuracy of my calculated power consumption by sampling the readings against the power meter feeding the heat pump and the averages are very close but instantaneous readings can be off by quite a bit.
17:43 Looks like that house doesn't even need 7kW in the middle of winter, but the owner accepted a 14kW unit, smh. I was told by both engineer and installer to get a 12kW unit... thankfully I don't have a trusting nature when it comes to such things, so I checked dedicated social media channels instead. Nerdy owners who use custom equipment to monitor their units and share the data on social media are exactly the kind of people you need to go to for advice, forget about installers and engineers trying to sell you units that they know precious little about (they might pretend to know by throwing marketing talking points at you, which is an indicator of ignorance). Instead of a 12kW unit, the nerdy owners told me to get a 6kW unit and to forget about buffer tanks and secondary pumps... they were far closer to the mark than the engineer and the installer. I went for an 8kW unit in the end, no buffer tank, no secondary pump, this unit is still a bit too big for my house, which became obvious in march when it started cycling. Fortunately, it's not horrendously oversized, unlike the units shown in the video, so the cycling can be considered normal. The SCOP is around 4, which I call a success, given the piss poor radiator installation the house has (narrow piping, all in series, just two rings for 9 radiators).
I think installers are worried about what happens on the coldest day, and no doubt one or two people will control their system badly (not keep the 'plates spinning'), and expect to heat up a house from cold on the coldest days. So, fitting a big one can be a safe bet for an installer. I'm sure that like you, many people would be better off with a smaller unit, on the other hand, a few would be miserable in the depth of winter. Not sure I share your trust of social metdia.. a lot of good advice, but just as much bad advice, and impossible for the uninformed judge between the two. I often get depressed when browsing FB. In the old days, the only cost effective heat pumps were small ones (like yours), and geberally these won't need buffers or complexity. I have a lot of experience of tiny heat pumps feeding big existing radiators, and all supported with woodstoves for the coldest days. If you browse, you will see refernce to small heat pumps 'straining'... not the case. heat pumps love heating tepid radiators. People need to make sure there isnt an electric boost in there somewhere. As you experience.. a lot better running, with less cycling, on average winters days... of which there are many.
@@johncantor4056 Hi John, thank you very much for making these videos, your calculators and taking the time to read comments and reply. Here in Spain many heat pump installers shove grossly oversized heat pumps down the customer's throat and, on top of it, blindly insist on buffer tank + secondary pump. If you tell them that you won't accept an oversized unit with an unnecessary buffer tank + additional pump, many refuse to do the installation, some even go as far as making you sign a waiver (they've watched too many lawyer movies 🤣). I understand that these companies are weary of clients who don't know how to run a heat pump system, so they err on the side of absurdity (and heftier bills... charging double of what they should and cashing in the EU subsidies that are meant for the customers). Anyway, one of the things that bothers me is that these companies don't bother running the numbers. For instance, I was repeatedly offered a 12kW unit despite the fact that my radiator installation could barely dissipate 6kW (assuming ΔT 30ºC). I don't know why I bothered making and sending those companies a detailed schematic of my home and radiator installation, they paid no mind to it. In the end I added 29 radiator elements (close to 2kW of extra dissipation capacity, just in case) and chose the 8kW unit, which turned out to be in the ballpark of what my home needed. A 12kW unit would've been beyond overkill, since my home needs around 6,6kW in the coldest hours of winter. Regarding social media, Facebook is the last place where I'd look for advice, I joined a Spanish Telegram channel dedicated to heat pump systems, over a thousand members, hundreds of heat pump owners sharing installation details and performance in a spreadsheet, technical manuals, schematics, tutorials, quotes, advice... pretty useful overall. But still, I didn't fully trust their advice either, they were telling me to get a 6kW unit and got an 8kW unit instead 😉 The only thing I'm worried about is the rather low flow rate I get when the 3-way valve directs the hot water towards the radiator circuit. I get ~670 liters per hour, when it should be closer to 1000 liters per hour, which I guess is caused by the narrow piping of the radiator circuit (16mm multilayer pipe, in series, only 2 rings, 60 radiator elements per ring). With this rather low flow rate, my unit is forced to increase its working ΔT to 7 or 8ºC (in order to output the same kW), instead of the ΔT 5ºC it's designed to work at. Do you think this is a problem I should be worried about? I can't change the piping of the radiator circuit, since that would involve destroying my home😩 I know it's not a problem with the Y filter, the dirt filter nor the unit, since the flow rate is nominal when the unit does DHW (3-way valve directs the hot water towards the DHW tank exchanger instead of the radiator circuit). Thanks again for your time and expertise!
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Thanks for interesting video. The latest inverter driven preheated scroll compressors are far less adversely affected by cycling than old tech reciprocating compressors. Also for latest heat pump models such as the Mitsubishi Ecodan R32, during periods of mild ambient temps and low heat demand, the auto adaptive management software prevents cycling by running at no less than minimum continuous power, allowing roomstat temp to overrun target temp by one degree of headroom, then switching off for however many hours are required for roomstat to cool back down by that one degree to target room temp, then the heat pump restarts again, and so on. Even for an oversized heat pump this avoids cycling altogether, so has no impact on efficiency. I have an oversized heat pump, being an 11.2kW model compared to design spec. recommendation of 8.5kW, but my performance stats are at least as good as manufacturer's data table specs. Also the 11.2kW is more efficient at exceptionally cold, high heat loads where the extra headroom is essential.
Brilliant. Watched this a few times since it was published and I notice something new each time. So helpful for understanding heat pumps. Thank you.
Thanks for your feed back. What else/ what topics do you think would be useful?
The issue of maintaining a high flow rate for heat pump efficiency seems to come up a lot in discussion groups, whether that’s expressed as pros and cons of buffers, zoning, or TRVs.
Brilliant. My take is there are plenty settings to find the optimum for your installation. That is reassuring, Thx.
John Cantor: Thank you.
I am just having my second winter with a heat pump and it is working pretty well - SCOP last winter was 3.6. However I have a feeling it could work better.
Once the external temperature rises above ~ 5 °C the heat output falls below ~ 2 kW - and the system cycles. This is ~ 40% of the nominal maximum output of a 5kW Vaillant Arotherm Plus pump, and like you said, I think that's just a choice by the manufacturer to set the lowest output at about 40% of maximum.
Understanding of what is going on is compounded by a complete lack of 'User Manuals', but I have concluded it is probably just not worth worrying about.
All the best
Michael
If it's cycling more than 3 times/hours, you may need a small buffer tank
@@hvacdesignsolutions Hi. That's possible. I do have a Low Loss Header, and I have been experimenting with changing the power of the pump which re-circulates water from the Low Loss Header through the radiators.
At current temperatures,(
Thank q very much for putting this video together very informative , I have recently had a quote for a 9 kw heat pump which I thought was two big ( I used actual heating usage data rather than calculated ) and got the size to 5-6 kw but this helps me a lot
I'm in the exact same situation. My WORST scenario in actual heating usage (calculatede on 6 years bills) is 4,5Kw, they quote a 8Kw heat pump that give 7,28 Kw @ -7/35 ... and my external project temperature is -5 so .... WHY???
@hardcard254 thanks. Re your flow rate, have you considered adding a pump in-line? So long as the extra pump is on a fixed speed setting, you should be ok. I have had 2 pumps in series on few occasions. The WiloPico with the green knob (not red) is great since the display shows watts, flowrate and also pressure.... Ideal for setting it up, and much easier than replacing pipework!
Thanks John, great analysis and troubleshooting. Good tips and advice on getting good performance.
Heat Pump manufactures have been slow to pick up on VFD compressor drives. Lots of advantages It will happen eventually
It's interesting to hear you mention a buffer tank @ 16:55, for the larger 16kW unit. Most installers I speak to, don't put them in. I wonder if thats because of the additional cost to the homeowner, or the installer doesn't understand how and when a Buffer Tank should be applied..........maybe something to consider for your next video.
Very interesting. 'Good cycling'' seems to be nothing to be worried about, notwithstanding start/stop wear on the compressor, however it should be remembered that fridges and freezers happily cycle throughout their lives and last an awful long time (generally they are retired for other reasons!)
Indeed, HP compressors 'soft start' these days, so wear & tear should not a worry
Late to the party, per usual🤔 What came to mind during this presentation, and thank you for your efforts and the knowledge you have provided; however, I was wondering if instead of heating the water that would flow through the system (pick your preference) would it make sense to have a large enough buffer tank(s) to provide the heated fluid and have the heat pump spend a longer period just bringing the buffer tank(s) back to their setpoint? If possible, would it make sense to design/install a system with a lead-lag buffer system for use?
Well... buffer tanks have been used in the way you describe for a long time. If space is available, yes, they can be a good idea. There are however a few down sides. Often, the average water temperature that the heat pump 'sees' is a few degrees higher than the emitters actually get. This rise tends to reduces to COP. Also, if the buffer is going to store any amount, it may need to rise several degrees above what is needed... e.g. a 200litres (typical size) tank , with 10kW heat input, would rise 10c (18F) in only 14 minutes, (using heatpumps.co.uk/calculators/ )
So buffer tanks need to be quite big if they are going to store a wothwhile abount. They also add a considerable expense and complexity. It may be worth it in some cases. Again, the majority of houses would probably prefer not to loose the space required for the tank.
Thank you - I think you've answered one of the questions that I had in mind - over-sizing is well known but under-sizing not so much it seems - what I was trying to understand is at which point in modulation the efficiency is highest and the EcoForest graphs seem to answer that - my thinking is that heat loss sizing is done for a -3C outdoor temp but actually in reality that only happens for a handful of days in the UK, which essentially means that the HP will not need to deliver as much heat on an 'average day' and thus be in the very low region of modulation, which could result in inefficiency and cycling too - so ideally, assuming the OEM has it programmed to not hit the very low modulation levels, the sweet spot for heat output versus heat loss is somewhere in the middle on an average day - or am I barking up the wrong tree? For very cold days, it may run at fullish output for longish periods rather than being scaled so that it only needs to run there at start up or on very cold days?
Mmm.. well, whilst that Ecoforest graph is interesting, maybe it could also be a bit misleading here since there are other factors (like water temperature) that are probably more important. e.g. whilst a 'small' unit might run at high revs a lot mid winter, it should also spend a lot of hours at mid speed, and it could probably run at lower temperature (less rest time). A big unit is likely to 'stray' into higher flow temperatures at times, and may spend a lot of the year cycling. How it's operated also has a bearing on things. e.g. if its fairly constant, or if it has long-ish rest times. Finding the best efficiency relating to unit size (wrt heat demand) seems hard to assess, and no doubt its the extremes that are the worry, and a region in the middle with similar performance. I think you are barking up a similar tree. Maybe theory and practice don't quite match since heating a house is a dynamic thing... (day/night), and all buildings and occupants are a bit different. Not sure if that helps!
@@johncantor4056 thanks yes that is helpful - as you say it's not clear cut and I was sort of comparing it to very "1 dimensional" controls on a gas boiler without weather compensation so hadn't considered water temperature aside from the assumption that if an "average" property has an 'over-size' condensing gas boiler, it can be dialled down to reduce the overall output, provided the rads can emit the heat, then it can happily output constantly at its lowest modulation, but if like one of the examples you showed, where little else was done and a 'like-for-like' HP replaces a gas boiler, it would be better to go smaller instead, but would that have a detrimental impact on the efficiency? I guess inverting HPs have a wider working range and so as you say avoiding those extremes is the key. Plus if done as a retro-fit without other changes like bigger rads and more insulation, those things can be done afterwards and thus erring on the smaller side would still be a better bet than worrying about those few days where the 'calculated' heat losses at -3C make people think they need to 'go large' in order not to feel cold...on those days, a smaller HP could easily just run continuously in a more efficient manner rather than the on/off manner of heating that so many people are used to in this country!
Surely the cop is very poor on a cold start before the compressor becomes warm and smooth ? One graph at 1355 shows a huge rise on a cold start ? Great video, thanks
You are right that COP at start (after a long rest) is poor as it warms everything up. Compressor would be warm though if starting when cycling is frequent. There is however another thing at play... at start-up, the compressor pressures are equal, so the compressor has a very 'easy ride' at first, until the pressure difference across the compressor builds up, so at start, if it were not for various inefficienies, the COP would be much higher at start up
Thank you for this wonderful information and clear presentation.
My system is a ducted Mitsubishi variable speed 36k BTU heat pump in Seattle WA USA where our cold temps are generally near 32 deg F but recently we had a week of 16 deg. 2700 sq ft house.
Given the goals of minimizing cycling and having our variable speed heat pumps run continuously at low flow temps;
If we like it cool at night can we turn the thermostat down in evening and then just heat very gradually in the morning by turning thermostat up 2 degrees at a time over couple of hours?
Does the heat pump measure the outside temperature and work harder / increase the flow temperature when it’s very cold outside? I notice air temps from my vents vary from 80-100 deg.
Does the heat pump work harder if thermostat set 10 deg over current room temp compared to only a set point of 2 deg higher; and does this harder work make the air flow temps higher?
Thank you for your generous work and presentation
Thanks for your comments.. I wish I could answer your question, but I dont actually know how the air-air control works. I would expect the system to register how many degrees the actual room temperature varies from the set-point , and respond accordingly... surely that is how it must work. i.e. as the room setpoint is approached, the compressor slows down, along with the fan speed. this gives the best comfoort. But does it also vary with respect to the outside temperature? I would expect it does. Given that a heat pump could give out twice the heat in mild weather compared to what it can give out in cold weather, then some sort of limitation for mild weather is surely part of the strategy. I would be interested to know.
Thanks, I think you’re right. Outside temp and temp differential (outside to set point) should be what the computer is most interested in. The heat pump must work harder if outside temp is cold and if your set point is a large jump up from current room temp; hence my theory of inching my thermostat up a couple degrees at a time as room gradually warms. Hopefully keeps compressor work light and air flow temp lower.
My rough estimate is my heat pump electricity consumption goes up about 3% for every degree I turn up the thermostat and also goes up 3-4% for every degree the outside temperature goes down. Either way it makes sense as I’m increasing the differential from outside temp to thermostat set point.
My electricity use was doubled with our recent week of 16 deg temp. House is old, could use better insulation, and Seattle homes not built for that.
Thanks again for interesting discussion
Steve
@@yt551217 In colder weather, the compressor will need to spin faster to get the same heat output, and in cold weather, more heat is needed, so surely it manages this intelligently in some way. Sounds like you are doing the right thing by increasing it slowly
Great video, very informative
You mention in this video at one point that maintaining the room temp slightly below the set point is ok. Is this just for a heat pump which can run continuous at low temps to balance the heat loss of the room/building? I have a gas boiler that I am running at low flow temps to determine if my property is "heat pump ready". I have been frustrated this winter that the set point is not being achieved but instead remains usually within 0.5 degs and the boiler cycles most of the day sort of balancing the heat loss of the room. I am probably being stubborn as I know the main living area has undersized radiators for low flow temps so this should be expected. I have smart controls so I am mostly disappointed the control cannot adapt and run the boiler for longer but due to smart TRVs I think this may be a limit of the system not having enough emitters at times and overheating rather than the controller.
I think I am getting at point that its generally better to keep the heat pump running in cold weather, so you dont really want the room thermosts turning it off... e.g. lets say it's running very happpily and steadily in cold weather (though might be interrupted by defrosts every say 40 mins). Anyhow, if the thermost turns it off, then there can be some catching up to do which may not be easy. Ideally the compressor will modulate down and keep running. The manufacturers thermosts is usually best, and this is where 'room target' or 'auto adapt' can work very well. In your case, I guess you are trying to vary/reduce the water temperure to see if say 40C is enough etc. Maybe your smart stats are trying to be too helpfull! can you simply turn the TRVs to max for your experiments?
Interesting video.
COP while important I think is often over emphasised.
COP I believe is analogous to a cars MPG, and what home owners really need to know is an equivalent to cost per mile - which changes with everyone's use case. Sticking with the car analogue- Getting a diesel with the best maximum potential MPG may not be the cheapest per mile option in the real world for someone who has to do lots of short journeys.
Yes I agree that COP is sometimes used too much (given too much 'weight'). Its actual energy use that's important. But lets say you improve all journey types by correct tyre pressures, then all MPGs might improve by say 10% for all... But, skewed as you say because diesels are not so good at short journeys. Its a matter of testing in relevant condition.
@@johncantor4056I would say the cost of energy to achieve comfort is most important since prices of power can vary significantly
Excellent stuff !! I am planing to have an Ashp installed, but not decided yet if Daikin or Panasonic. Nevertheless, I plan to have also a 200 liter buffer installed (for defrosting and to reduce on/offs). My question would be how the buffer should be installed? In series or in parralel ? Thanks!
Thanks Adrian. I suggest your first enquiry about configuration should be with the manufacturer. They will have worked through buffer options, and how it relates to their particular controls and they will have sensor positions in mind. I have seen a few very bad buffer tanks where a lot of unwanted mixing happens inside them, so there are pitfalls to avoid. e.g. where to get 35C at your radiators, you need 40C at the heat pump. In this case, dropping the COP considerably. If it's only system volume for defrost that is the worry, then a small 2-pipe volumiser seems a good idea to me. I have never understood why manufacturers don't start defrost in the normal way, and if there isnt enough heat in the radiator circuit, it briefly diverts to DHW. This should 'steal' only a tiny bit of DHW heat, and only in certain conditions. Anyhow, each heat pump has different requirements, so you need to refer to the manufacturers recommendations.
mind of a genius
Hi John, Thanks for this informative video. I have an LG Therma V Monobloc R32 9kw heatpump and I see it cycles time to time working for about 30-40 mins and waiting for another 5-10 mins and cycling again. I understand that it's not a problem, but still struggling to understand why it overshoots the target temperature but instead not gradually slowing down while reaching the target temperatures. Should I be worried? (I have a 300lt DWH tank and 100lt buffer tank, radiators are connected to this buffer tank with a cycling pump and my tado is controlling this cycling pump, not controlling the Heatpump)
Hello. I'm wondering if this 'cycling' is actually defrosting. This can happen about as you describe, and will a lot in cold damp conditions. Actually worse when say 0C to +5C. Nothing to worry about. If you catch it stopping, you should see the white frost on the fins melt over a few minutes. Otherwise, in this weather, the unit is likely to run steadily. They generally vary (modulate) between 33% and 100%. When the heat demand is lower, (milder weather) it will need to cycle, and cycling on/off mid range can sometimes be better than running steadily at 33%. difference between the two is often slight.
John, very interesting, though I am an engineer and try to make sense of my 7kw Vaillant heat pump, if I show you my Ubibot flow temp-in at the buffer tank for a week, would you be able to comment? not sure if you have an email I can send the data to? myVaillant app is showing a SCOP between 4-4.5 with my heat curve set at 0.8 and max flow temp at 45 and min at 25degC, would like to know if you can see the suggested back in the amount of cycling my heatpump does? cheers Mark
I'm curious what the difference there would be with longer cycle times - Ecodan controls have a setting of 10-60 mins which I assume is a forced off period (doesn't seem clear in manual) - I'd hope you'd minimise those refrigerant start up losses and see some benefit of the low system temperatures on restart with longer off periods and hence (hopefully) longer on periods?
Yes, its not clear in Ecodan info, but I think the 10-60 is related to time response of room sensor. I guess some 1/2hr rests should result in some better COP due to cold start, BUT it will 'rev up'. Shame there is not an 'economy' setting, maybe watching outside temperature, that would stop it going to maximum speed so eagerly.
@@zlmdragon. I have never quite understood this setting. There seem to be other factors at play. Of course the actual compressor speed is all important, and I found the 6kW 'revs up' unnecessarily even when its quite mild out. I expect some 'rev ups' are there to help compressor lubrication, but I still find it straying to high output, unlike the older models. I guess there are 2 main considerations a) ensure that enough heat is being delivered, b) minimise running cost. It seems to be programmed mainly for 'a'
Thanks
Fantastic stuff
Hi John
I have a heat pump which is oversized I believe our heat pump daikin atherma 3 is 9kw and our design temp is 5kw @-2. The heat pump will module to about 30% I am told but this would still be too high in the spring/auturm months. Would a buffer help with the efficiency? We currently have a 25litre but was thinking of upping it to a 90L based on a calculation I got off google. This is piped as a LLH with a secondary circulation pump. Any help would be greatly appreciated.
Hello Roman. You can look at my calculator at heatpumps.co.uk/calculators/ to help assess buffer sizes. It might be useful. It's not that straightforward because lets say your 9kW Daikin actually only drops to say 4kW in milder condition, and all is in steady-state and happy, then if you need to cycle, as the radiators rise above the temperature you need, then unfortunately, it wont re-start at 4kW again. Instead, it will 'rev-up' a bit, possibly to 9kW for a short while before it slows down again. (I actually don't have much experience with Daikin) So, to be clear, the buffer volume will slow down the rate of water temperure rise, so it should help, but there are more than one way to configure a buffer tank, of which small details like the sensor positions is important. You are adding complexity. I suggest you go with Daikin's recommendations because they will have developed their controls to work in a certain way.
Unless you have ground heating or a large / complex installation, it's likely that you don't actually need any buffer tanks or secondary pumps.
Find out whether your installation meets the water volume requirement for your HP on its own, without the 25 litre buffer tank... if it does, get rid of it and get rid of that secondary pump too.
Your COP is likely to improve.
Hi John, Thanks for your videos, I have a 10 year old Daikin ASHP and I would like to monitor it more closely, its doesn't have any interface to allow me to see what its is doing. I notice that the openenergy monitor uses heat meters to measure the flow and returns temperatures, I would love to do that but those devices are very expensive. Is it possible to do something similar using DS18B20 sensors (or similar) taped to the main flow and return and use these to estimate the energy? I have a feeling that there is good reason why this would not work but I would like to know if there is a cheaper way of adding some better monitoring to my ASHP. Thanks
Yes, heat meters too expensive for most people. I think a lot can be gleaned from sensors on pipes. The heat (kW) is proportional to flow-return dt. IF flowrate constant. e.g. if you look at my graph at 2:40 in, and measure (with a rule) the dt at 27C point and 29.5C point, I make it 16mm and 15.5mm.. so the dt has reduced a tiny bit, but input power has increased, so COP a bit worse. This is just an example of what you might be able to glean. However, if water flow changes, this is meaningless, so you need to do specific experiments, and repeat a few times.
@@johncantor4056 Thanks John I will try and put something together. Its a shame that heat meters are so expensive.
@@timcx I’ve got a hitachi yutaki I’m trying to get to grips with in terms of flows and cycling. It doesn’t have good data output either, I’ve recently found home assistant and Shelly iot devices. You need a bit of IT skills but you can get a lot of info from Shelly em and some temp sensors.
I'm doing exactly this- flow, return and a current clamp on the HP power. Very useful to set up the system indeed.
@@simoncanfer5030 Hi Simon how are you collecting the temperatures, what equipment are you using? I was thinking of using EmonTx but open to other ideas.
What is the best water's delta T for ASHP? I see that COP estimator says if dT is higher, condensing coefficient is also higher and COP gets lower.
There are too many dts! If the flow-return dt is large, then the condensing temperure is likely to be closer to the flow temperure, BUT the system is worse off because the mean temperature to the heating system is worse... I think this needs spelling out with a sketch... thanks for highlighting it. The COP estimator is fairly simple. I tried to make a version to include flow-return dts, but it became unnecessarily complicated!
@@johncantor4056 Yeah, with lower flow rate dt we can get higher medium temperature and it means that we can use lower LWT. But on other side if lets say we apply dt = 5 for cold weather, than for moderate weather dt can be 2 or even 3 and heat pump can start cycling. I am just playing with configs of my heating system and trying to get the best SCOP. My heat pump can't work constant with dt < 3.5(that's for moderate weather that I have 90% of time). In this case LWT starts to raise as heat pump starts to increase frequency. And it can just work with higher LWT(1-2 higher than needed) or starts to cycling. Can't find any info if it happens due to algo on my heat pump, or it's physical limitation of process that happens inside condenser. Maybe if dt is too low, gas can't transfer to liquid on 100% and that's why heat pump starts to increase output (some kind of protection).
For now seems I need to make dt 4-5 for moderate weather and 8-10 for really cold weather. Or make a variable flow rate.
Maybe it's also the limitation of compressor speed that you mentioned in the video. I see that it avoids to work with frequency less than 35-40% and power consumption less than 20% of max.
The estimator assumes a certain flow temperature, and if the flow-return dt changes, (assuming same heat (kW), then the flowrate must be changing, and return temperature is changing too. An alternative would have been to give a 'mean' flow-return temperature, and this might be more relevant to water-to-refrigerant dt. I somehow need to spell this out better because as it stands, it looks like you can change the 'offset' and change the COP, however, the 'offset' is more a function of heat-exchanger size/compressor speed than anything else. I am pondering it.
Its a bit complicated since many systems have a fixed flow circ pump, so typically, if flow-return dt is 5 at high power, then it will naturally become 2.5 when the system is 1/2 power. Other systems simply 'track' the flow and return temperatures, and they adjust the circ pump automatically so the flow-return dt stays at 5 degrees (kelvin/Celsius). Furthermore, some systems might assume a fixed flow, and the control uses the dt value as control in some way. That might seem all a bit daunting, but I dont think fine-tuning of dt will actually affect the COP much. However, if the dt is 6 or more then the return is getting cold, so the flow temperure may need to be warmer to compensate, so for that reason, a large dt is rarely desirable.
There’s a lot to digest in your video. Thanks for posting it. Here’s a video where I examine the performance of my own heatpump: th-cam.com/video/QAKLrVAdvQ0/w-d-xo.htmlsi=H3oZ9isini3LlF93
I came to different conclusions as to why my COP was getting worse for higher ambient temperatures, but since that video I’ve gotten even newer insights into my heatpump performance. What I’m seeing is that flow return delta T is shrinking from 4 degrees to 1-2 degrees during milder weather and warmer room temps leading to bad COP. But when the house is warming up from cold following a vacation, the COP is much higher. So I’m wandering if actually my radiator TRVs are the culprit, despite being on the maximum end stops. I’m wandering if they are closing in anyway
Hello Anthony.. i look forward to watching your video through ( no time right now!!).. One initial question.. how accurate do you think your heat assessment is when dt is less than 2? A small sensor error will make a big difference. with no heat, bit pump running, what dt is showing on the heat meter? Is it zero? I will watch your video soon,
@@johncantor4056 Hello John I find the flow sensor minimum reading is 6.5l/min (which is also what the manual says) and the next lowest reading is 7.1l/min so that’s just over 10% error. Likewise when it comes to the primary current reading for the compressor the lowest readings are 0.5, 1.3, 1.8, 2.3 Amps etc… There’s absolutely no variation in between those discrete readings. What this means is very choppy current and flowrates and therefore very choppy instantaneous coefficients of performance. However when you average it out over the course of 10 minutes then you get some quite revealing trends happening, I tend to use 10 minute averages to determine what’s going on with my heat pump. DeltaT temperatures are accurate to within 0.1 degrees on both the flow and return temperatures. I am able to determine the accuracy of my calculated power consumption by sampling the readings against the power meter feeding the heat pump and the averages are very close but instantaneous readings can be off by quite a bit.
17:43 Looks like that house doesn't even need 7kW in the middle of winter, but the owner accepted a 14kW unit, smh.
I was told by both engineer and installer to get a 12kW unit... thankfully I don't have a trusting nature when it comes to such things, so I checked dedicated social media channels instead.
Nerdy owners who use custom equipment to monitor their units and share the data on social media are exactly the kind of people you need to go to for advice, forget about installers and engineers trying to sell you units that they know precious little about (they might pretend to know by throwing marketing talking points at you, which is an indicator of ignorance).
Instead of a 12kW unit, the nerdy owners told me to get a 6kW unit and to forget about buffer tanks and secondary pumps... they were far closer to the mark than the engineer and the installer.
I went for an 8kW unit in the end, no buffer tank, no secondary pump, this unit is still a bit too big for my house, which became obvious in march when it started cycling.
Fortunately, it's not horrendously oversized, unlike the units shown in the video, so the cycling can be considered normal.
The SCOP is around 4, which I call a success, given the piss poor radiator installation the house has (narrow piping, all in series, just two rings for 9 radiators).
I think installers are worried about what happens on the coldest day,
and no doubt one or two people will control their system badly (not keep
the 'plates spinning'), and expect to heat up a house from cold on the
coldest days. So, fitting a big one can be a safe bet for an installer.
I'm sure that like you, many people would be better off with a smaller
unit, on the other hand, a few would be miserable in the depth of winter.
Not sure I share your trust of social metdia.. a lot of good advice, but
just as much bad advice, and impossible for the uninformed judge between
the two. I often get depressed when browsing FB.
In the old days, the only cost effective heat pumps were small ones
(like yours), and geberally these won't need buffers or complexity. I
have a lot of experience of tiny heat pumps feeding big existing
radiators, and all supported with woodstoves for the coldest days.
If you browse, you will see refernce to small heat pumps 'straining'...
not the case. heat pumps love heating tepid radiators. People need to
make sure there isnt an electric boost in there somewhere. As you
experience.. a lot better running, with less cycling, on average winters
days... of which there are many.
@@johncantor4056
Hi John, thank you very much for making these videos, your calculators and taking the time to read comments and reply.
Here in Spain many heat pump installers shove grossly oversized heat pumps down the customer's throat and, on top of it, blindly insist on buffer tank + secondary pump.
If you tell them that you won't accept an oversized unit with an unnecessary buffer tank + additional pump, many refuse to do the installation, some even go as far as making you sign a waiver (they've watched too many lawyer movies 🤣).
I understand that these companies are weary of clients who don't know how to run a heat pump system, so they err on the side of absurdity (and heftier bills... charging double of what they should and cashing in the EU subsidies that are meant for the customers).
Anyway, one of the things that bothers me is that these companies don't bother running the numbers.
For instance, I was repeatedly offered a 12kW unit despite the fact that my radiator installation could barely dissipate 6kW (assuming ΔT 30ºC).
I don't know why I bothered making and sending those companies a detailed schematic of my home and radiator installation, they paid no mind to it.
In the end I added 29 radiator elements (close to 2kW of extra dissipation capacity, just in case) and chose the 8kW unit, which turned out to be in the ballpark of what my home needed.
A 12kW unit would've been beyond overkill, since my home needs around 6,6kW in the coldest hours of winter.
Regarding social media, Facebook is the last place where I'd look for advice, I joined a Spanish Telegram channel dedicated to heat pump systems, over a thousand members, hundreds of heat pump owners sharing installation details and performance in a spreadsheet, technical manuals, schematics, tutorials, quotes, advice... pretty useful overall.
But still, I didn't fully trust their advice either, they were telling me to get a 6kW unit and got an 8kW unit instead 😉
The only thing I'm worried about is the rather low flow rate I get when the 3-way valve directs the hot water towards the radiator circuit.
I get ~670 liters per hour, when it should be closer to 1000 liters per hour, which I guess is caused by the narrow piping of the radiator circuit (16mm multilayer pipe, in series, only 2 rings, 60 radiator elements per ring).
With this rather low flow rate, my unit is forced to increase its working ΔT to 7 or 8ºC (in order to output the same kW), instead of the ΔT 5ºC it's designed to work at.
Do you think this is a problem I should be worried about?
I can't change the piping of the radiator circuit, since that would involve destroying my home😩
I know it's not a problem with the Y filter, the dirt filter nor the unit, since the flow rate is nominal when the unit does DHW (3-way valve directs the hot water towards the DHW tank exchanger instead of the radiator circuit).
Thanks again for your time and expertise!