Most effective way of heating using an air source heat pump (ASHP)

themorganator4

Hi all,

I have an ASHP for heating and hot water and want to know the most effective way of using it.

Currently the heating is set at 17.c between 3am and 12am the next day, hot water comes on at 1am so I need a 2 hour gap before heating comes on (as apparently it will take forever if it is doing both simultaneously.) 
Now the temp set on the HP is 55.c which means that once the water used to supply the rads hits 55.c it turns off, now I was thinking of reducing this to 30.c which means it will heat up very quickly and the COP would be at it's most efficient but I don't think 30.c would be warm enough to heat the house to 17-18.c so it would be running constantly. Maybe a sweet spot of 40-45.c? 

my other half works from home so there is always someone in. 

Any advice welcome. 

matelodave

55c is quite hot for a heat pump - it's just on the edge of switching in the back-up/boost heater. The optimum is 35 degrees but you might find that's a bit to low, especially when its everso cold outside

Personally I'd tweak it down to 40 for a few days to see what effect it has on it's power consumption and heating recovery times and then adjust up or down by only one or two degrees untill you feel its about right 

What ever you do, keep a record of the tweaks and their effects and remember it will take a couple of days for the system to settle down after you've made any adjustments. - having a fiddle every hour or so wont tell you anything. Dont forget to take into account the outside temperatures - the consumption and efficiency varies a lot depending on the weather especially at this time of the year when it can change by 5-10 degrees just in one day.

You might wish to have a shufti at this thread which has been running on a similar subject to get a few ideas. Even though its skewed towards underfloor heating the general principles of running a heatpump are the same - run it at the lowest temperature you can get away with, even it it seems to run for ever https://forums.moneysavingexpert.com/discussion/6219931/most-efficient-way-to-run-underfloor-heating/p1.

I find mine is best with weather compensation turned on - it averages around 35 degrees, but goes up to just over 40 when its very cold and down to just over 30 when it's around 10-12 outside.

A bit more info on your setup would be helpful, make & model of the heatpump,  how is it controlled, radiators, underfloor etc.
You question was a bit like - "I've got a car, I drive it at 55, what will happen if I drive it at 30"

Cardew

Low water temperature and ASHP operating for long periods is the principle - 24/7 incurrent cold snap.

themorganator4

matelodave said:

55c is quite hot for a heat pump - it's just on the edge of switching in the back-up/boost heater. The optimum is 35 degrees but you might find that's a bit to low, especially when its everso cold outside

Personally I'd tweak it down to 40 for a few days to see what effect it has on it's power consumption and heating recovery times and then adjust up or down by only one or two degrees untill you feel its about right 

What ever you do, keep a record of the tweaks and their effects and remember it will take a couple of days for the system to settle down after you've made any adjustments. - having a fiddle every hour or so wont tell you anything. Dont forget to take into account the outside temperatures - the consumption and efficiency varies a lot depending on the weather especially at this time of the year when it can change by 5-10 degrees just in one day.

You might wish to have a shufti at this thread which has been running on a similar subject to get a few ideas. Even though its skewed towards underfloor heating the general principles of running a heatpump are the same - run it at the lowest temperature you can get away with, even it it seems to run for ever https://forums.moneysavingexpert.com/discussion/6219931/most-efficient-way-to-run-underfloor-heating/p1.

I find mine is best with weather compensation turned on - it averages around 35 degrees, but goes up to just over 40 when its very cold and down to just over 30 when it's around 10-12 outside.

A bit more info on your setup would be helpful, make & model of the heatpump,  how is it controlled, radiators, underfloor etc.
You question was a bit like - "I've got a car, I drive it at 55, what will happen if I drive it at 30"

Thank you, very useful.

The HP is an ideal airtherm 4.5 KW (i think that is heat output and not consumption, i believe consumption averages to about 1.5kw) it is plumbed in to radiators in a central heating system (i.e not underfloor) and is controlled by a honeywell controller and a room thermostat (set at 18.c) I can adjust the temp on the HP to a max of 55.c (I have taken it down to 40.c as per you advice) 

Mouldymeat3

Did the installer do the standard calculations to estimate the heat demand and size the radiators accordingly?  I note from the data sheet that it apparently produces DHW at 65C without an immersion heater, unusually high!

matelodave

4.5kw is pretty small for a heatpump so I guess you've got a small and extremely well insulated dwelling. Bear in mind that the lower you wind the temperature down, the longer it will take for the place to reheat because its the radiator that dissipate the heat into the rooms. Lower temps mean less heat which is OK proving you are still dissipating sufficient to off-set the heat loss from the room. Dropping your flow from 55 to 40 could reduce the rad outputs by around 30% or more.