Water source heat pump operating condition 2

[oooaaa]

I am confused by the water source heat pump operating conditions.

in 2000 Ashrae system and equipment handbook, chapter 8, it mentions that in order to operating satisfactorily, the air entering the water source heat pumps should be above 60 deg. F. Therefore, the ventilation air must be preheated in cold climates. As I understand, it is talking about the heat pump in heating model. However, from some sources I find that the operating limits of entering air temperature for water source heat pump could be as low as 40 deg. F. Shall I must preheat the entering air to get mixing air temperature to 60 deg. F in heating model?
For the water source heat pump roof top units,
either trane or carrier do not have the preheat coil operation, does it mean that they are not suitable for cold climate application?

 

[AbbyNormal]

With that cool of an entering air temperature, you will use up all your space heating capacity to warm the mixed air up to close to room temperature. Nothing left to cover the space heat.



Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[oooaaa]

Both Trane and Carrier water source heat pump roof top unit do not have preheat coil option, is this type of unit a good application in cold climats like Canada? What's the advantage and risks using water source heat pump roof top units instead of interior installed water source heat pumps?

 

[ChrisConley]

I'd say freezing would be a major concern with the rooftop mounted equipment.

Not to discount the handbook, but what you really need to do is figure out how much heat you need to account for heat loss, add the heat required to heat your ventilation air and then find a heat pump that can handle the load.

Having said that, I prefer to handle ventilation with a dedicated unit (gas fired heater, hot water coil, whatever). You can more easily encorporate heat recovery in a central unit.

Then duct tempered air to your heat pumps. The heat pumps provide zone level control and you don't need to worry about very cold air coming into the space when the heat pumps aren't running. The level you need to temper to would be determined by the capacity of the heat pump.

The above is based on a -40 deg design condition.... much, much harder to find a heat pump that can take air from -40F to 90F.