13 degrees! is that a typo? who installed that?

Posted by: @alastair

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All opinions and pointers welcome as I don't want to spend if I don't need to, and all it might need is a system tweak somewhere that I am unaware of.

Cheers

0.5 C per hour is quite fast.  

14kW is enormous, how big (floor area) and what construction is your house

Increasing emitter size is almost always good.

Before you spend any money, how is your heat pump controlled, is it on 24x7, have you balanced the emitters, are you using trvs?

Hi.

We have a 112 m2 year-2000 built standard box.  We were originally told that we'd have an 11kW heat pump but on the day of installation we found out it was a 14 kW unit. We were told that it would be fine - maybe we should have questioned this more but the installer said it would make the heating easier. Our heat pump is controlled using a Salus thermostat for turning the heat pump on and off, and each radiator is controlled using TRVs. 

To be clear, the drop in temperature at the rate I mentioned is when the heat pump is off, and the outside temperature is 8C or less. We have draught proofed everything we can think of, have new windows and doors, have cavity wall insulation and double the recommended depth of roof insulation. We just cannot think why the rate of heat loss is so quick.... We have air bricks so the only thing we can think of is that the heat is lost through the floor somewhere, but a thermal camera survey doesn't show anything obvious. Thank you for confirming that a rate of 0.5C/hr is at the higher end - we also thought it was a bit high! 

Posted by: @alastair

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Thank you for confirming that a rate of 0.5C/hr is at the higher end - we also thought it was a bit high! 

Its nothing to do with the heat pump of course, something about the house.  It could just be that its very low heat capacity (which can happen if all the brickwork etc is external to the insulation) so even with a low loss cools quickly.

Posted by: @alastair

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We have a 112 m2 year-2000 built standard box.  We were originally told that we'd have an 11kW heat pump but on the day of installation we found out it was a 14 kW unit.

11/14 doesnt matter if its Daikin, all the 9+ ones are identical hardware, all of the 8- ones are identical hardware, they just software limit the output.

However with that house you should only need a 5kW heat pump!  

Posted by: @alastair

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Our heat pump is controlled using a Salus thermostat for turning the heat pump on and off, and each radiator is controlled using TRVs.

Thats about the worst way possible to run a heat pump (they should generally be run 24x7 without TRVs or thermostats on a weather compensation curve) however if you are happy with the cost and comfort not to worry

Do you know how much energy you use (or better still how much the heat pump reports it delivers to the house) in a year, or on any given day of the year?

Apart from the high rate of temp drop is there anything concerning you?

Posted by: @jamespa

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they should generally be run 24x7 without TRVs or thermostats or a weather compensation curve

@jamespa did you mean ... ON a weather compensation curve rather than OR?

Posted by: @andrewj

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Posted by: @jamespa

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they should generally be run 24x7 without TRVs or thermostats or a weather compensation curve

@jamespa did you mean ... ON a weather compensation curve rather than OR?

Yes, sorry.

Posted by: @alastair

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We have draught proofed everything we can think of, have new windows and doors, have cavity wall insulation and double the recommended depth of roof insulation. We just cannot think why the rate of heat loss is so quick.... 

That's a similar sized house to mine, also fully insulated, which also loses about 0.4/0.5c per hour on average.

I can only think that we lose heat through the floors, which I admit have not been upgraded in any way since being laid.  Where we have laminate flooring the actual floor can feel very cool to the touch.  

@alastair, in short, no, increasing emitter capacity won’t harm the heat pump. In fact, in most cases it does the opposite. Bigger or additional radiators give the system more surface area to emit heat, which means the heat pump can meet demand at a lower flow temperature. Lower flow temps generally equal better efficiency and a more even, comfortable heat output. Adding a second radiator to a room where replacement isn’t practical is a perfectly valid approach.

What you’re describing, the house being “warm enough” but not really cosy, is borderline emitter sizing or a heat distribution issue. Living rooms and main bedrooms tend to feel OK because they often have the biggest radiators and longest occupancy, while other rooms lag behind. That usually points to distribution and emitter balance rather than a fundamental heat pump problem.

Before spending money, I’d double-check a few basics. Make sure all radiators are properly balanced, that TRVs aren’t fighting the system and that the weather compensation curve isn’t set too conservatively. A small tweak there can sometimes make the whole house feel noticeably better without touching hardware. That said, if one or two rooms are consistently underperforming, targeted emitter upgrades are usually money well spent IMO.

If you want to share current flow temps, weather comp settings and which rooms are struggling most, people here can probably help you decide whether this is a tweak job, an emitter job or a bit of both.

A quick Google search showed that building regulations have required floors to be insulated since 1990, so you should have some.  However, your floor insulation is probably not to modern standards.

If I may say so, your problem definition is a bit vague.  You say the house doesn't feel cosy, except for the lounge and the bedroom.  Does that mean you are feeling drafts, or is the temperature is too low throughout the house, or are some rooms too cold, or something else?  If you increase the thermostat temperature does it feel cosy then?

As mentioned above, a thermostat and TRVs are not the ideal way to run a heat pump.  We are running our house with the thermostat set to 30C.  I have adjusted the weather compensation curve so that the temperature in the hall is about 20C, regardless of the outdoor temperature.

We have the problem that some radiators are not getting hot enough and upstairs is about 21C, which is a bit too hot.  I am slowly adjusting the radiator return valves to reduce water flow in some rooms.  This is resulting in increased flow in other rooms that we want to be warmer.  

Unfortunately, we have a few radiators that still won't get warm.  Even turning off the whole of upstairs and most downstairs radiators, the lounge radiators still had a low flow rate.  This is probably due to sludge in the pipes or radiators, or possibly due to poor pipe work design.

The lesson I am gradually learning is that you need to get your present system working as well as possible, before potentially wasting money upgrading components that are already adequate.

I have cleaned my magnetic filter and I plan to continue balancing radiators.  I will probably have a power flush in the new year.  You might consider doing the same.

@grahamf Another possibility that may be worth trying… Close the LSV(s) slightly in the room with the temperature sensor so that the heat pump runs slightly longer and or slightly hotter to maintain the desired temperature in that room. In doing so, more energy will be available to the emitters in the other (cooler) rooms. Any rooms that then show too great a rise might have their LSV’s shut a little. I know this sounds counterproductive when you may be trying to reduce the flow temp but if you have cold rooms, this may solve the problem. I am not talking of throttling the system which you desire to be as open as possible but just re-directing some heat to where it presently fails to reach. Regards, Toodles.

@toodles interesting suggestion, thanks.  I will try to resist the temptation to hijack someone else's topic to solve my problems!