What size is my heat pump

EletricMan

Hi guys trying to work out the KW of my heat pump, any help greatly appreciated.

The first picture is the outside unit. The second is the inside unit.

Thanks

2011

I the first photo shows a unit that has a load of 3.49kW. Internally this unit has a 1.79 kW compressor (included in the 3.49 kW load).

The second photo shows a unit that has a load of 5.80 kW. This is the sum total of 3 internal loads:
- Unit auxiliary heater, 3 kW
- Tank auxiliary heater, 2.75 kW
- Pump, 0.05 kW

As the above loads all all maximums the maximum combined electrical load would be considered to be 3.49 + 5.80 = 9.29 kW

Bruthal

Yes so the compressor is 1.79kw as said.

Aux heat loads are 3kw and 2.75kw.

In effect they are just like immersion heaters, as a supplement or backup to the heat pump if it is not working etc, and so are not in use during normal heat pump operation.

I suspect that the heat transfer capacity of that system is 7.5kw or so. I seen a cop (coefficient of performance) of 4.6 for a similar one, so the compressor load of 1.79 x 4.6 = around 8kw.

(COP is the output /input basically)

So the heat pump refrigeration circuit can extract and transfer 7-8 kw of heat from outside to inside, using 1.79kw to do so.

2011

Bruthal wrote: »

In effect they are just like immersion heaters, as a supplement or backup to the heat pump if it is not working etc, and so are not in use during normal heat pump operation.

That’s interesting, I did not know this. I have never connected this type of unit up. This is reaffirms the fact that it is important to read the installation manual carefully so that the requirementS are fully understood.

I suspect that the heat transfer capacity of that system is 7.5kw or so. I seen a cop (coefficient of performance) of 4.6 for a similar one, so the compressor load of 1.79 x 4.6 = around 8kw.

.......and this is where heat pumps are fundamentally different from electric heaters. They produce more heat energy than they consume in electrical energy.

(COP is the output /input basically)

....correct only when the input = the electrical input. The other “input” is from the temperature of the outside air.

Bruthal

2011 wrote: »

That’s interesting, I did not know this. I have never connected this type of unit up. This is reaffirms the fact that it is important to read the installation manual carefully so that the requirementS are fully understood.

Yea they are just backup heaters I would imagine.

.......and this is where heat pumps are fundamentally different from electric heaters. They produce more heat energy than they consume in electrical energy.

I would say they more transfer already existing heat than produce any. Its like having a hot spring and using a pump to pump it to rads in a house. Except this is using refrigeration to extract heat through evaporation, and re-release it through condensing.

....correct only when the input = the electrical input. The other “input” is from the temperature of the outside air.

The COP would be the work required, compared to the heat delivered.
Lower air temperatures outside affect performance overall, as the compressor will run for longer to maintain the inside temp against a lower outside one.

People buying and installing them want to know the power input for a given output.

So the kw input/kw output over time will give the COP. So its enery in/energy out.

In theory it shouldnt drop below 1. It might though, but at or near 1, electric heaters may as well be used.

EletricMan

Next question, I obviously want this unit to be efficient as possible in heating my house. So would I be right in saying if this unit was under sized (which I think it is) it would need the aux to help in heating the house? Which isn't Ideal and would increase the bills and decrease the life span of the unit if it's over working?

2011

Bruthal wrote: »

The COP would be the work required, compared to the heat delivered.

People buying and installing them want to know the power input for a given output.

Sure.

I'm being pedantic

My point is that if output/input is > 1 it suggests that it is possible to break "the law of conservation of energy". Whereas in reality heat pumps are exactly as you put it, i.e. "more transfer already existing heat than produce any". COP is what it is all about, otherwise we may as well just use electric heaters.

John.G

EletricMan wrote: »

Next question, I obviously want this unit to be efficient as possible in heating my house. So would I be right in saying if this unit was under sized (which I think it is) it would need the aux to help in heating the house? Which isn't Ideal and would increase the bills and decrease the life span of the unit if it's over working?

I have seen that a figure of 2.8 might be reasonable to assume as the seasonal coefficient of performance or SCOP so a 8kw unit which is based on 7C/35C (air/water) with a COP of ~4.0 would "average" ~ 5.13 kw, if running 24/7 which is the recommendated way, then based on my own 4 bed detached house would be just about sufficient but I would feel more comfortable with a 12 kw unit with a VSD compressor, it all depends on how well insulated etc that your own house is??.
Just quoting a Kingspan 8 kw unit here (file too big to download) then this gives a flavour of COPs and outputs.

air/water output COP
degC Kw
7/35 7.19 3.92
2/35 5.41 3.00
0/35 5.14 2.95
0/45 5.11 2.42
0/55 4.88 2.2
table not aligning but you can see what I mean.

Also I will post a link in a few minutes which gives a lifetime of reading re users heat pump experiences which is very interesting.

here you go 97 pages of pure enjoyment!
https://www.boards.ie/vbulletin/showthread.php?t=2055433218&page=97

Also go to bottom of page 2 "electricity used for heat pumps"
https://www.seai.ie/publications/Domestic-Fuel-Cost-Comparison.pdf

Tuco88

Whats the overall opinion on heat pumps? Are they only good for new builds...

Former Coach

Thinking of Air-to-water system. Can anybody advise on whether night-rate meter is advisable?

2011

Tuco88 wrote: »

Whats the overall opinion on heat pumps? Are they only good for new builds...

I listened to a talk about them in the RDS given by a expert. He said that if the home is not at least A2 rated (in terms of BER) they won’t work. I believe him as he was selling them and by making this statement he was telling most of the audience that their homes were not suitable.

I know a few people that have them in their nice shiny new homes (A3 rated). They seem to be very happy with the result. These units run a lot of the time producing a low grade heat. Underfloor heating and oversized radiators are the norm for these systems.

Tuco88

I suspected if you didn't have a good BER or at least upgraded insulation on the house it wouldn't be cost effective.

Gas is probably still the best option in such case... And a stove for most homes.

In regards to a retro fit, take a home with an oil boiler with no zones. I would take it the heating circuits could stay(Radiator Loops)..Anybody know what kind of work would be required? Very roughly now, what would be involved new hot water cylinder ect???

John.G

I fitted a pipe stat to my OFCH this AM set to reduce the flow temp to a measured 42C,
with all rads i/s and a ambient of 6C/5C, and house already heated up. I am maintaining 21C in all d/stairs rooms and 17C u/stairs, I calculate that my rads are running at 21% of their rated (50C) output and my 20 kw boiler was on for 23.1% of the time which means that 3.7 kw (allowing 80% boiler efficiency) is satisfying my house heating requirements (HW not included). I have a 4 b/room cavity BLOCK semi and normally require ~ 11/12K kwh/annum (net) to satisfy heating and HW requirements.
Based on this, then one might get away with the present rad sizing if running a HP 24/7, my system will be off overnight so I will see how long, if ever, it takes to get the room temps back up in the morning, normally 1 hour will do the trick with boiler SP at 75C.

autumnalcore

Never understood the assertion that heat pumps were not suitable in less than BER A2.

Look at scandanavia, canada and eastern europe houses made of timber / cementboard cladding glasswool and toilet roll inserts.

Sweden has millions of heatpumps installed and average house is 158kwh/m2/year

Canada is closer to 200kwh/m2/year

If there is a problem its more likely to be undersized units with low duty cycles and unnecessarily complex electronics giving marginal gains in COP over a likely reduced life span.

Bruthal

autumnalcore wrote: »

Never understood the assertion that heat pumps were not suitable in less than BER A2.

Look at scandanavia, canada and eastern europe houses made of timber / cementboard cladding glasswool and toilet roll inserts.

Sweden has millions of heatpumps installed and average house is 158kwh/m2/year

Canada is closer to 200kwh/m2/year

If there is a problem its more likely to be undersized units with low duty cycles and unnecessarily complex electronics giving marginal gains in COP over a likely reduced life span.

Maybe it's often air sourced being talked about or assumed. If the evaporator was immersed in a hot spring, or temperature stable ground, it likely will be more productive than in - 30 air.

2011

autumnalcore wrote: »

Never understood the assertion that heat pumps were not suitable in less than BER A2.

I am far from an expert on this. I did talk to a few experts (one from Mitsubishi) and this was their view.

I also installed the electrics for a heat pump in a large home that had insulation that is lacking. Electricity bills are through the roof.

Remember these units produce a low grade heat.