Fan Coil Units for use with a (cooling) ASHP

[saveasteading]

23 minutes ago, JohnMo said:

soak aways are huge, compared to normal

I'm interested.

The regs show ever bigger areas where permeability is poor.

On sand they don't seem to acknowledge that the water won't reach the end. 

 

So in our case we used perforated pipes heading different directions to spread it.... phase 2 and 3 extensions to the zone, the drawings and calcs got us the approval, but are 'yet' to go in.

[joth]

23 minutes ago, JohnMo said:

Set up to run long run for periods, this helps a lot. Plus our ambient outside helps. 

And down-sizing the ASHP to allow these long runs at a low  deltaT without short cycling, isn't it?
Our ASHP is way oversized so will bordering short cycle (5 min runtime, 10min period) when just cooling the slab to ~16deg.

I'm still getting COP of 3.5-4. But it's powered from PV - if I could double the COP it would give me about 30p more SEG payments per day on these hottest days.  

 

[JohnMo]

5 minutes ago, joth said:

And down-sizing the ASHP to allow these long runs at a low  deltaT without short cycling, isn't it?
Our ASHP is way oversized so will bordering short cycle (5 min runtime, 10min period) when just cooling the slab to ~16deg.

I'm still getting COP of 3.5-4. But it's powered from PV - if I could double the COP it would give me about 30p more SEG payments per day on these hottest days.  

 

Last year on our 6kW heat pump it cycled, depending on load, we averaged around 4 to 5 CoP over the day depending on a few factors doing cooling. This year with a 4kW it can run low and slow, our dT was about 2.5 degs. Yesterday's whole day CoP was 7.3 including standby time/energy.

 

We only cool if there is solar gains, so we have plenty of PV also. So it free. It would almost always get clipped from PV also, if we weren't using it, so it really is free.

[Michael_S]

Not sure if we can calculate an EER, we have a heat meter but not sure if it counts backwards.....

 

Gonna add some more fans to the rads and overvolt them a bit to see if we can get some more airflow - I know you can get actual sit on rad units but the fans are less than a quid each compared to about £100 for a unit that will only do about 1/3 the length of a fad and is probably louder too.

 

Currently we are using our second hand heath robinson heat pump - hoping to move to a 'proper' set up but MCS sound rules mean our preferred placement is max 55db that seems to strictly limit the number of 8-10kw units available and the one that seems to be best fit (Grant) does not cool. 

 

Does anyone know of any other units that fit the 8-10kw and 55db or less sound power criteria and do cooling?  Thanks

[JohnMo]

1 hour ago, Michael_S said:

Not sure if we can calculate an EER

It's the inverse of CoP, so if calculating CoP you just get a negative figure, exactly the same calculation. Take the negative away you get EER.

[Michael_S]

8 hours ago, JohnMo said:

It's the inverse of CoP, so if calculating CoP you just get a negative figure, exactly the same calculation. Take the negative away you get EER.

The heat meter measures the flow rate and flow and return temps and calculates a kwh heat transferred number which normally just increases like an electricity meter.  Not sure if the return is warmer than the flow if it will decreases the total kwh transferred counter. 

Edited 12 hours ago by Michael_S

[JohnMo]

7 hours ago, Michael_S said:

calculates a kwh heat transferred number which normally just increases like an electricity meter.  Not sure if the return is warmer than the flow if it will decreases the total kwh transferred counter. 

It calculates kW as either a positive or negative dependant on heating or cooling. The kWh heat delivered scale is exactly the same as electric meter, it only adds it doesn't run backwards. So in cooling the kWh counter stays static 

 

7 hours ago, Michael_S said:

heat meter measures the flow rate and flow and return temps and calculates a kwh heat transferred number

Not exactly correct, it calculates kW then adds a time function to get kWh.

 

Heat pump monitor software has a tick box in the settings to allow it to understand if you also do cooling and it runs an internal timer to distinguish between cooling and defrosting. Once timer elapsed it knows you are in cooling mode and attributes the correct CoP, SCoP values 

[SteamyTea]

On 27/05/2026 at 01:02, Gus Potter said:

It totally reverses the dew point calculation and yes you do get condensation forming on the cooler house surfaces

Why in the Southern States the VCL is on the inside.

Mind you, with climate change affecting the regional weather patterns, there may need to be some rethink about condensation risks.