Reverse cycle condensing unit

[Ashby]

Hi all

New here so bear with me. Does anyone know what the minium air on coil is for a dx coil in a AHU when operating in the heating/reverse cycle mode in winter (eg. in winter can we use full fresh air at -4 deg c on to the coil). I heard that it was around +10 deg c minimum. We are looking to use a full fresh air AHU with the addition of a seperate heat pump condensing unit.

[Brian_UK]

It depends on what conditions the equipment was designed for.

With hot water heating coils you would expect, if I remember correctly, the pre-heat coil to lift the air temperature up to around 8 or 10°C.

Sorry, forgot my manners - welcome to the forum.

[BritCit_Juve]

If you are using 100% fresh air you need to put in a preheater if you are using a crossflow heatexchanger to recover heat from the extract and a post coil heater to boost the air temperature in very low ambients especially if there isn't much roomload.
The coils will need careful design as they will be subject to wider load variation than a standard split with low temp air on the condenser coil causing overcondensing in winter and high temperature in heating causing high evaporating temp.

Brit

[Ashby]

Thanks for your replies - much appreciated