Turbo compressor has more temperature lift than the turbo fans, if the system requires 25 F temp rise, one compressor will do the job instead of two turbo fans. Consequently reducing in equipments investment. Is my assumption right?
You are correct that one (1) turbo compressor will achieve a comparable compression of heating vapors (~ 25°F temperature rise) as compared to two (2) turbofans operating in-series. The reasons we find value in using the two (2) turbofans in-series versus just one (1) turbo compressor are: a) The initial capital cost and delivery timing of the two (2) turbofans are comparable to that of just one (1) turbo compressor. b) Our customers report significantly lower routine annual maintenance costs, and downtime for unscheduled maintenance, for turbofans as compared to a turbo compressor. c) The motors of the two (2) turbofans combined consume approximately the same electrical power (KW/hr) as the motor of one (1) turbo compressor (since they are achieving the same total vapor compression duty). d) The turbo compressor often requires a gear set to achieve required impeller speed (typically ~ 2x increase to the motor shaft speed) for its vapor compression duty, while turbofan impellers rotate at the same speed as the motor shaft (often in 4,500 to 6,000 RPM range). The gear set increases compressor maintenance complexity and costs as compared to turbofans. e) Turbo compressors achieve their high compression ratio due to tight clearances between the impeller and the inside surfaces of the impeller housing. This makes turbo compressors prone to “surging” issues if suction vapor flow decreases below compressor design rate, causing cavitation on the suction side of the compressor impeller. Customers have found “compressor surging” can actually cause building structures to shake (in-addition to the associated loud sound generated), and if allowed to continue too long can result in a catastrophic failure of the compressor’s impeller. We know of several cases where a compressor impeller failure dangerously sent metal shrapnel thru the compressor hosing into the surrounding production area. This surging issue can be addressed by recycling some discharge vapor flow back to the suction inlet of the compressor, but at the expense of reduced electrical power efficiency. Turbofans do not experience this surging phenomenon. The larger clearance between the impeller and the housing allows vapor to “slip” from the impeller discharge side back to the impeller suction side, preventing suction side cavitation. Turbofan impellers also rotate at ~ ½ the speed of a compressor impeller, and have not been know (as far as I am aware) to mechanically fail sending shrapnel thru the housing. In the end, the customers where we have replaced one (1) turbo compressor with two (2) turbofans in-series have told us they would never go back to operating a turbo compressor.
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Turbo compressor has more temperature lift than the turbo fans, if the system requires 25 F temp rise, one compressor will do the job instead of two turbo fans. Consequently reducing in equipments investment. Is my assumption right?
You are correct that one (1) turbo compressor will achieve a comparable compression of heating vapors (~ 25°F temperature rise) as compared to two (2) turbofans operating in-series.
The reasons we find value in using the two (2) turbofans in-series versus just one (1) turbo compressor are:
a) The initial capital cost and delivery timing of the two (2) turbofans are comparable to that of just one (1) turbo compressor.
b) Our customers report significantly lower routine annual maintenance costs, and downtime for unscheduled maintenance, for turbofans as compared to a turbo compressor.
c) The motors of the two (2) turbofans combined consume approximately the same electrical power (KW/hr) as the motor of one (1) turbo compressor (since they are achieving the same total vapor compression duty).
d) The turbo compressor often requires a gear set to achieve required impeller speed (typically ~ 2x increase to the motor shaft speed) for its vapor compression duty, while turbofan impellers rotate at the same speed as the motor shaft (often in 4,500 to 6,000 RPM range). The gear set increases compressor maintenance complexity and costs as compared to turbofans.
e) Turbo compressors achieve their high compression ratio due to tight clearances between the impeller and the inside surfaces of the impeller housing. This makes turbo compressors prone to “surging” issues if suction vapor flow decreases below compressor design rate, causing cavitation on the suction side of the compressor impeller. Customers have found “compressor surging” can actually cause building structures to shake (in-addition to the associated loud sound generated), and if allowed to continue too long can result in a catastrophic failure of the compressor’s impeller. We know of several cases where a compressor impeller failure dangerously sent metal shrapnel thru the compressor hosing into the surrounding production area. This surging issue can be addressed by recycling some discharge vapor flow back to the suction inlet of the compressor, but at the expense of reduced electrical power efficiency.
Turbofans do not experience this surging phenomenon. The larger clearance between the impeller and the housing allows vapor to “slip” from the impeller discharge side back to the impeller suction side, preventing suction side cavitation. Turbofan impellers also rotate at ~ ½ the speed of a compressor impeller, and have not been know (as far as I am aware) to mechanically fail sending shrapnel thru the housing.
In the end, the customers where we have replaced one (1) turbo compressor with two (2) turbofans in-series have told us they would never go back to operating a turbo compressor.
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