Air to Water Heat Source Pump - Sizing

[lenny]

HI Guys

I have a client who wants underfloor heating sourced by air to water heat pump. The underfloor heating suppliers have come back with a heat loss of 20kW for the underfloor system as a whole. Does this mean that I need a heat pump of this size ?

I am waiting to hear back from the manufacturer of the heat pumps but thought some existing installers may be able to advise accordingly.?

Also , anoyone got any feedback on these heat pumps CTC - Eco Air range ?

Many thanks

Len

 

[fuzzy]

im no expert but i think the heat pump gives out 3 times what it uses. therefore you would need a 7kw air source to give you an output of 21kw if this is correct

 

[lenny]

Thanks fuzzy

I dont think thats right what you are saying, If the outside temperature was -5 then the cop may only be 2/1, that would leave me 6kw short when I need it most.

Is it possible to get a cop of say 1.5/1 from an air to water heat pump at -15? If this is possible would a 14kw unit be the right size for a property that requires 20kw?

Help!!!!!!


Len

 

[eaton]

Please don't do it as above, it all depends on the manufacturer you choose to how their heat pump copes at differant levels. It's not a case of 20kw so let's just chuck in a 7kw. You'll need to know what the underfloor has been specced as also ie 45wm2 or 35wm2 etc

 

[fuzzy]

Thanks fuzzy

I dont think thats right what you are saying, If the outside temperature was -5 then the cop may only be 2/1, that would leave me 6kw short when I need it most.

Is it possible to get a cop of say 1.5/1 from an air to water heat pump at -15? If this is possible would a 14kw unit be the right size for a property that requires 20kw?

Help!!!!!!


Len

sorry thats the limit of my knowledge. when i asked the question some time back i was told the kW quoted refered to how much energy the air source uses. therefore you need to use a correction factor which uunder normal conditions is x3. i worried this didnt seem vey helpful as you are never sure of output which is the most improtant thing. if you find out please let me know

 

[Eco Heat]

You would need to have a survey done on your property to assertain the correct heat load and then the pump would be sized accordingly. The heat load will depend on various factors such as windows insulation etc. also the amount of extract fans in the property has an impact on the heat loss.

 

[peteheat]

You would need to have a survey done on your property to assertain the correct heat load and then the pump would be sized accordingly. The heat load will depend on various factors such as windows insulation etc. also the amount of extract fans in the property has an impact on the heat loss.

I agree, while it never made me popular with potential customers I refuse to have anything to do with fitting a heat pump unless they gave me accurate heat loss calculations.

To get the best out of any heat pump they need to insulate to a level that will shock most other builders, air tightness is another big issue, heat recovery / mechanical ventilation is another, and most important from the plumber / installers point of view is good quality heating controls (I prefer step back thermostats).

Have fun.

 

[blakeecotec]

Hello, I am MCS regsitered for heat pump and assessed to be compliant to the lastest MIS3005 standard . A 24kW single phase heat pump is avaiable, but this is 24kW at 7 degree air temp. It will drop to about 16-18kw at -3 degrees dependant on the flow temp. The heat pump output will need to be known at -3degrees and what ever flow temp the underfloor has been design for.

If you base your heat loss on a new build at around 40W to 45W/square metre then you won't be far off on sizing. To meet requirement of MIS3005 a full heat loss calcilation must be done, the underfloor guys have usually done this if you have a plan from them. The hot water load will also need to be worked out, 40 ltrs/person/day, so about 0.5kw/person.

Heat pumps do not flow share, they heat the hot water and then switch back to the heating. Typically DHW load adds 2kW to the heat requirements. But this house sound big, so probably 3kW.

What I would do, if only single phase powerb is avaialble and the load is 22kW load is have two heat pumps. Panasonic do a total capacity heat pump that has a guaranteed output to -15 degrees. So two of these 12kW units would work. Maybe even a 12kW and a 9kW. If you have two floors, then one heat pump 12kW for the ground and the other 12kW for the first floor and DHW. Panasonic also don't need a buffer tank and have soft start inverter drive, so no problem with start currents etc..

 

[markfxy]

Panasonic may say it doesn't need a buffer tank but I would always fit one although slightly smaller for an inverter.