I bought a Heat Pump

Reed_Richards

Meatballs said:

Keep dropping it slowly until it no longer meets the heat demand then pop it back up  

I agree with the strategy but the latest change I made dropped the target Leaving Water Temperature by up to 4 C for outside temperatures of 5 C and greater so I will stick with what I have for a few weeks until I am sure it does meet the heat demand.  This will also give me more time to estimate whether it is making a difference to my overall consumption.

shinytop

@Reed_Richards, are you using the room thermostats and weather compensation? That's the way my ASHP was set up by the installers.  As @Meatballs says, keep playing around with it.  What I think will happen though is that if you lower the flow to the level I do, i.e. enough to heat the house running constantly, then when the room thermostat forces the ASHP to stop, it will take a long time to warm the house when it calls for heat again.  I stop the ASHP for 5 hours at night and it takes a while to heat the house up again.

But I've been experimenting again.  For the past 4 days I've been running the system with thermostats and with the flow set at a constant 45C.  I don't have a lot of data yet and it hasn't been very cold but my initial modelling (!) suggests I'm using 25% or more energy than before.  I'll post some more detail when I have it. 

Reed_Richards

Yes, I am using the room thermostats on my two zones to control the temperatures and weather compensation (which my LG ASHP calls "AI") to moderate the Leaving Water Temperature.  And I will always do this because I don't want my house to be at a constant temperature for all 24 hours of the day.  But I turn the heating off (well set back 3 C) at night and increase the set room temperature slowly during the day so temperature inside the house will probably vary in a way that is quite similar to yours, @shinytop (prior to the latest experiment).

michaels

Reed_Richards said:

I have been simultaneously massively impressed and a little horrified by @shinytop's method of controlling their heat pump using finely-tuned weather compensation and abandoning the use of a room thermostat.  This is not something that Mr and Mrs Average would either want or need to do ( @Cardew ) but it's probably the right way to eke out every last drop of efficiency that a heat pump can provide.

It has inspired me to be more ambitious with my weather compensation settings.  I now have

Outdoor temperature:           Min 1 max 19
Leaving Water Temperature: Max 50 Min 26

50 C is the maximum LWT specified on my MCS certificate and this target temperature will be used if the outside temperature is 1 C or lower.
If the outside temperature is 19 C or higher the target LWT would be 26 C.
Otherwise there is a linear relationship so if the outside temperature is 10 C (half way between 1 & 19) then the target LWT would be 38 C (half way between 50 & 26).   So far this has proven to be sufficient to keep the house warm with the outside temperature at 8 C or below.  It means that the target Leaving Water Temperature is lower than it used to be which, in principle, should give me greater efficiency.  It's hard to be sure if this is working because the outside temperature is never constant.  But the peak power per cycle of the heat pump seems to have dropped.       
      

Our gas boiler with weather comp controls has no room stat, we just set the heating curve level and slope and the trvs control individual rooms, the boiler modulates input from 19kwh down to 4 kwh in order to maintain the return temp based on the weather comp curve and the required room temp (day or might choices only and the actual temp will depend on the curve setting not the number set on the 'dial').

Reed_Richards

michaels said;

Our gas boiler with weather comp controls has no room stat, we just set the heating curve level and slope and the trvs control individual rooms, the boiler modulates input from 19kwh down to 4 kwh in order to maintain the return temp based on the weather comp curve and the required room temp (day or might choices only and the actual temp will depend on the curve setting not the number set on the 'dial').

Can you give a few more details please, as I don't really follow.   

Any radiator-based heating system could potentially use only TRVs (although there needs to be provision for what happens if all the radiators are shut off by their TRVs).  If the outside temperature increases then you don't need your radiators to be as warm to maintain the same inside temperature, the basis of Weather Compensation.  The gas boiler in my old house did this by reducing the water temperature.  I thought the main point of doing this was to allow more or better condensing for greater efficiency so to get the return temperature as low as possible rather than to maintain it.    

Treehuggger999

The thing that worries me about air source heat pumps is the cost of maintenance. It is well known that air source heat pumps are not as efficient as ground source heat pumps. I am wondering if you will make enough saving over the years to cover the cost of maintenance before the whole thing needs to be replaced. ( I am not taking account of installation as you would have had to put some form of heating in). Basically the heat pump is a fridge condenser in reverse ( a lot of refrigeration suppliers are going into making them) and just as a fridge has to work harder when it is hot outside, a heat pump has to work harder when it is cold outside. So it works least well when you need it the most.
I hope it works out for you, it is a problem in rural areas to get cheap clean heating.

michaels

Reed_Richards said:

michaels said;

Our gas boiler with weather comp controls has no room stat, we just set the heating curve level and slope and the trvs control individual rooms, the boiler modulates input from 19kwh down to 4 kwh in order to maintain the return temp based on the weather comp curve and the required room temp (day or might choices only and the actual temp will depend on the curve setting not the number set on the 'dial').

Can you give a few more details please, as I don't really follow.   

Any radiator-based heating system could potentially use only TRVs (although there needs to be provision for what happens if all the radiators are shut off by their TRVs).  If the outside temperature increases then you don't need your radiators to be as warm to maintain the same inside temperature, the basis of Weather Compensation.  The gas boiler in my old house did this by reducing the water temperature.  I thought the main point of doing this was to allow more or better condensing for greater efficiency so to get the return temperature as low as possible rather than to maintain it.    

Yes, the return temp is set based on the outside temp.  As the TRVs turn off in individual rooms the return temp goes up and the boiler modulates down to achieve the return temp consistent with the outside temp.

As long as the return temp doesn't exceed the condensing threshold then you get peak efficiency; the boiler stays on as long as possible at the lowest setting needed to keep the flow temp rather than having to cycle on and off.

Verdigris

How often do you have your fridge serviced? Heat pumps are inherently low maintenance. GSHPs are only more efficient because the heat source is at a near constant temperature. ASHPs have to cope with a range of air temperatures but are optimised at 7 degrees air temp, 35 degrees flow temp, so you can compare, like fuel efficiency in cars, which is tested at a constant 80kph/56mph.

matelodave

Treehuggger999 said:

The thing that worries me about air source heat pumps is the cost of maintenance. It is well known that air source heat pumps are not as efficient as ground source heat pumps. I am wondering if you will make enough saving over the years to cover the cost of maintenance before the whole thing needs to be replaced. ( I am not taking account of installation as you would have had to put some form of heating in). Basically the heat pump is a fridge condenser in reverse ( a lot of refrigeration suppliers are going into making them) and just as a fridge has to work harder when it is hot outside, a heat pump has to work harder when it is cold outside. So it works least well when you need it the most.
I hope it works out for you, it is a problem in rural areas to get cheap clean heating.

TBH there's not really any maintenance required - as said above, how frequently does anyone have their fridge serviced. Gas and oil boilers need far more service than a heatpump. Mine is now eleven years old and although it's had a couple of services (to ensure safety for the non-vented water tank) it's only had one problem and that was with a flow switch (the same as they have in gas and oil boilers) which I fixed myself.

As I've said before there are too many myths around that are being promulgated by those who know nothing about them.

JKenH

matelodave said:

Treehuggger999 said:

The thing that worries me about air source heat pumps is the cost of maintenance. It is well known that air source heat pumps are not as efficient as ground source heat pumps. I am wondering if you will make enough saving over the years to cover the cost of maintenance before the whole thing needs to be replaced. ( I am not taking account of installation as you would have had to put some form of heating in). Basically the heat pump is a fridge condenser in reverse ( a lot of refrigeration suppliers are going into making them) and just as a fridge has to work harder when it is hot outside, a heat pump has to work harder when it is cold outside. So it works least well when you need it the most.
I hope it works out for you, it is a problem in rural areas to get cheap clean heating.

TBH there's not really any maintenance required - as said above, how frequently does anyone have their fridge serviced. Gas and oil boilers need far more service than a heatpump..

Rightly or wrongly, my oil boiler has not been serviced since 2008.