Thank you for the explanation. Few questions I have are in regard to the direct cooling using the DOAS for latent cooling and an indoor AHU for air circulation and sensible load. Since the DOAS will be providing 100% OA and the AHU circulating air: 1. Would this create and over pressurize space? 2. How is the CFM balancing done? 3. Should there be an additional relief fan?
Of course whatever air that is brought in using the DOAS will have to have a corresponding exhaust or relief. This all depends on the design criteria for each of the spaces receiving Ventilation air. This is similar to a unit using an economizer. There are several examples in the videos related to economizers and the DOAS unit. Depending on the space requirements you can use the DOAS to pressurize a space or create a negative pressure by exhausting more than is supplied.
This is my first time learning about the DOAS system. So basically it is tempering & conditioning the outside air by filtration & use of a heating/cooling coil that is being directed to a space. A fan coil unit or other device is in the space to handle the bulk of the heating/cooling load but the tempered air from the DOAS provides high quality ventilation & reduces the work load of a fan coil, etc. Is my understanding correct on this?
The DOAS can be used to handle the latent load, while leaving the sensible load to the terminal units. DOAS units are used in many applications, such as hospitals, Gymnasiums, Schools, Laboratories, Etc. They are used to Comply with ASHRAE 62.1 ventilation requirements, and can be used with energy recovery where applicable. They are commonly used in VRF systems, as most of these Fan Coils can't handle much latent load.
Ok, got it. The latent load taken care of in the DOAS system is to dehumidify the ventilation air & the terminal units in the space lowers the temperature or increases it therefore taking care of the sensible load. I’m really enjoying this channel !
In the VRF system- if the cassette is off/not calling, will the DOAS continue to supply outside air or will it only give air to the room when the thermostat calls?
You would need a control damper to shutoff ventilation air to a space if that spaces AC unit was off, and have a VFD on the DOAS unit to slow down the fan when pressure built-up in the ventilation supply duct.
Depending on occupancy schedules and space zoning, there are various system options. Only the engineer who is familiar with the particulars of the project can decide what the best system is for the building and how its planned to be operated.
We never learned about the DOAS in school, so your video was a big help indeed!
Glad it was helpful. Thanks for watching.
Thank you for the explanation. Few questions I have are in regard to the direct cooling using the DOAS for latent cooling and an indoor AHU for air circulation and sensible load. Since the DOAS will be providing 100% OA and the AHU circulating air:
1. Would this create and over pressurize space?
2. How is the CFM balancing done?
3. Should there be an additional relief fan?
Of course whatever air that is brought in using the DOAS will have to have a corresponding exhaust or relief. This all depends on the design criteria for each of the spaces receiving Ventilation air. This is similar to a unit using an economizer. There are several examples in the videos related to economizers and the DOAS unit. Depending on the space requirements you can use the DOAS to pressurize a space or create a negative pressure by exhausting more than is supplied.
This is my first time learning about the DOAS system. So basically it is tempering & conditioning the outside air by filtration & use of a heating/cooling coil that is being directed to a space. A fan coil unit or other device is in the space to handle the bulk of the heating/cooling load but the tempered air from the DOAS provides high quality ventilation & reduces the work load of a fan coil, etc. Is my understanding correct on this?
The DOAS can be used to handle the latent load, while leaving the sensible load to the terminal units. DOAS units are used in many applications, such as hospitals, Gymnasiums, Schools, Laboratories, Etc. They are used to Comply with ASHRAE 62.1 ventilation requirements, and can be used with energy recovery where applicable. They are commonly used in VRF systems, as most of these Fan Coils can't handle much latent load.
Ok, got it. The latent load taken care of in the DOAS system is to dehumidify the ventilation air & the terminal units in the space lowers the temperature or increases it therefore taking care of the sensible load. I’m really enjoying this channel !
Well explained with great presentation. Thanks!
You're Welcome
In the VRF system- if the cassette is off/not calling, will the DOAS continue to supply outside air or will it only give air to the room when the thermostat calls?
You would need a control damper to shutoff ventilation air to a space if that spaces AC unit was off, and have a VFD on the DOAS unit to slow down the fan when pressure built-up in the ventilation supply duct.
Great video ! A lot of nyc projects I have worked on used the last method presented on the video
Thanks
Very well presented. Thank you for sharing. I have given you a thumbs up and subscribed.
Thank You
THANK YOU FOR THIS VIDEO IT HELPS ME UNDERSTAND DOAS WITH VRF UNIT COMBO VERY WELL
You're Welcome
Wonderful explanation
Glad you liked it. Thanks for watching.
My designer is not using a chiller for a 10000 SF single story bldg? Doas is piped into conditioned space. AC is from a DX.
Depending on occupancy schedules and space zoning, there are various system options. Only the engineer who is familiar with the particulars of the project can decide what the best system is for the building and how its planned to be operated.
WOW, Its very informative
Glad you liked it. Thanks for watching.
Such a great video. Thank you for posting this.
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Awesome video
Thanks
Very useful thanks please make more vedioes.
Thank you, we will.