Extra heat sources impact on HP

zxzxzx

I have an A2A HP and a log burner in my lounge. I am having a wet HP system fitted, what will be the impact of using the first two on the third?

As an example, I light the log burner at night and the room temp (door closed) might hit high twenty c’s, how will that impact on the rest of the house?

Netexporter

It won't significantly affect it, as long as the main thermostat is in a "neutral" space, so unaffected by additional heat sources, assuming you don't have thermostatic radiator valves. If you do have TRVs, open them fully and balance each room individually, with the lock-shield valve, and then let the weather compensation do the rest.

If you're having underfloor heating then balance the rooms at the manifold(s).

matelodave

As said above, if you have the main thermostat  (if you use one) in the room with auxiliary heating then it will affect the rest of the place but it wont if the stat is in an area unaffected by the additional heat source. So be careful where you locate any additional stats. Likewise dont use TRV's as they really upset the system balance and can cause low flow issues and increase stop/start cycling of the heatpump which increase both wear and running costs

A wireless stat that can be shifted around may well be the best option so you can find the optimum location, although generally if the system is set up properly and you've got weather compensation carefully tuned you dont really need a room stat.

The extra heat in the room will mean that there's less heat dissipated by the radiator or u/f heating in that room so the unit may well be a little more efficient but its probably not going to make much of a difference

wrf12345

Be more interesting if you could vent the other heat sources into the new heat pump and then get the benefit of its COP...

zxzxzx

…..the very thought of explaining that I am opening the lounge widow and building an air tunnel to improve COP fills me with abject fear.

QrizB

wrf12345 said:

Be more interesting if you could vent the other heat sources into the new heat pump and then get the benefit of its COP...

Putting aside the practical aspects, that's not how it works.

Imagine you've got a heat pump with a COP of three. This means that one kWh of electricity put into the heat pump will draw two kWh of heat from the ambient conditions to give three kWh of useful heat. Great.

Now imagine that those two kWh of ambient heat had themselves come from a heat pump with a COP of three. To produce them, you'll have used 0.67 kWh of electricity. So the "three kWh of useful heat" that you get out will have cost you 1.67kWh of electricity.

That's an overall COP of 1.8, far worse than you had to begin with.

There are times when stacking heat pumps makes sense, but it's not a way of improving COP.

matt_drummer

As a point of interest

All of the heat produced by an air source heat pump is extracted from the air.

In the above example 3kWh of heat is extracted from the air and the 1kWh of electricity consumed is just compressing the refrigerant, the electricity consumption produces no heat at all other than the mechanical heat generated by the compressor.

All 3kWh of heat (energy) is extracted from the ambient air conditions.

If you could feed an ASHP with warmer air, in this example from the chimney say, the efficiency would improve. I am not suggesting that it is practical though!