Air cooled Heat pump Fan behaviour

[blaluq]

I have measured air flow in an air cooled heat pump in summer season and winter season, and I have found that air flow is much greater in winter than in summer (2200 m3/h in summer vs 3700 m3/h in winter), when I've always thought it was the opposite.

I believed it was much higher in summer, because in winter the coils acts as an evaporator, then there is water reducing the air flow surface and air density and viscosity is higher and the pressure drop increases. But in fact, as air density is much higher in winter, maybe that's the reason in my experiments I have found that actual heating season flow is higher than summer season.

But does anybody know if this is the actual reason?

Thanks everybody, and best regards

 

[ChrisConley]

My guess is you are measuring actual air flow. Air in the winter is denser and as a result if your fan is moving 1000 scfm, the actual amount of air will be higher than 1000 scfm in the summer. The 's' in scfm stands for standard temperature and pressure, and is usually ommitted. I don't have the formula on me, but you can calculated acfm (actual cfm) from scfm given actual temperature and pressure.

 

[imok2]

We know that that the amount of BTU removed is a function of air flow, so it stands to reason that when we are in the heating mode and the OSA is 35*f ; if we increase the amount of air flow across the evaporator(condenser) we will get greater performance.
It may be that you have a 2 speed or a VFD condenser fan motor. The capacity and the efficiency of a heat pump depend upon adequate airflow. There should be about 400 to 500 cubic feet per minute (cfm) airflow for each ton of the heat pump's air-conditioning capacity. Efficiency and performance deteriorate if airflow is much less than 350 cfm per ton.

 

[vinod68]

you can use the below formula to calculate acutal sm3/hr (Nm3/hr) from am3/hr

Actual M3/Hr =

(Nm3/Hr x (273 + measured temp. deg. C)) / 273

considering that there is not much pressure difference.
The pressure difference is basiclayy due to the altitude.

Or the standrad formula is

(P1V1)/T1 = (P2V2)/T2