I bought a Heat Pump

michaels

Where does your circuit 'start' - we had a problem with the furthest upstairs rads not getting hot but managed to solve it eventually by closing off the flow to the downstairs rads using the lockshields - and as mentioned above strangling the flow to all the other rads via the TRVs to get the circulation going in the first place then working backwards.

TheMaster_2

michaels said:

Where does your circuit 'start' - we had a problem with the furthest upstairs rads not getting hot but managed to solve it eventually by closing off the flow to the downstairs rads using the lockshields - and as mentioned above strangling the flow to all the other rads via the TRVs to get the circulation going in the first place then working backwards.

I think I am going to try more messing about with the TRVs upstairs and see what happens, will wait for a good solar day so its free!

matelodave

It's pretty obvious that you've got a problem downstairs if the flow temp entering the rads is so much lower than upstairs and that the temp drop across them is so much greater.

I'd have though the best time to sort the rads out is when it's cold and you are trying to balance them properly with the maximum temperature drop across them, rather than on a warm sunny day day when the rads and heatpump dont need to work very hard.

Waiting for the sun to shine to save a pound or two when you need it to work when its cold, rather than worm sounds a bit strange to me - just my opinion you understand.

Reed_Richards

matelodave said:

I'd have though the best time to sort the rads out is when it's cold and you are trying to balance them properly with the maximum temperature drop across them, rather than on a warm sunny day day when the rads and heatpump dont need to work very hard.

Where I am today, it is bright, sunny and absolutely freezing.  So that would satisfy everybody.

matelodave

It was overcast and snowing here when I sent my message - not a lot and the out side temp was 3 degrees. It's a bit sunnier now but very windy and cold.

Reed_Richards

It is now 6 months since my heat pump was installed so I thought I would provide an update on how it is performing and how it compares to my old oil boiler.  As a reminder, I have a 12 kW air source heat pump supplying a bungalow with 16 radiators of which 12 are new (10 replacements, 2 additional).  It also heats my hot water cylinder.

The ASHP got off to a shaky start as it ran for about a day then stopped working with an error message.  This was scary but I now know that it happens so frequently that installers are advised to warn customers of the possibility.  It was a blocked filter and my installer came back very promptly and fixed it.  Thereafter the only other problem since was a small leak as the majority of the pipework was new (we rerouted it from under the floor to the loft).  Again my installer returned very promptly to deal with this.

My heat pump has its own meter so I know exactly how much electricity it has consumed.  Up to and including 9th June this is 5296.45 kWh.  In fact it consumed more than half of this in the first two months of use (3106.74 kWh to 12th February).  I think this is mostly due to this being the coldest time of the year but a little due to the fact that I kept the house about a degree warmer than usual over this time to build up confidence that I could.  However my other half kept complaining that it was too hot so I went back to as near normal as I could (given a change of room thermostat).

The best data I have for my old oil boiler was from 4th February 2019 to 6th February 2020 when it consumed 1936 litres of oil at a cost of £870.  That works out at an average of 41.9 kWh per day if you assume 90% efficiency and the standard 10.35 kWh per litre of oil.  By comparison my current average for the heat pump is 28.75 kWh per day BUT we are just coming into summer now and my average for June has been 1.34 kWh per day.  So I feel I have a fair chance of beating my £870 target figure for a full year's electricity at my current tariff.  And that would be for a winter and spring that were a good deal colder than the year for which I have the oil boiler data.

For both the heat pump and the oil boiler I set back the night time temperature by a couple of degrees so the heating is off at night unless it is very cold.  I then step up the temperature during the day so it is warmest in the evening when we are most sedentary.  The room thermostat is in the living/dining area with TRVs on the radiators elsewhere.  My new thermostat came with a "comfort mode" which would aim to reach an increased set temperature at the start time set for that temperature and I used that.

Overall I am pleased with the heat pump as it has replaced the oil boiler with little noticeable difference for heating.  The heat pump itself is not noisy in operation, similar to the exhaust from the oil boiler although probably more at low frequencies.  The worst noise is from the central heating pump in the airing cupboard and only because it is audible at all - similar to the pump with the gas boiler in my old house.  My oil boiler was external with its own pump and this was completely silent inside the house.        

shinytop

Thanks for the update.  I'm about 3 months behind you with a very similar house/installation.  My ASHP numbers are similar to yours but my target to beat is about double so I'm well on track.

matelodave

Thanks for the info - it's good to see that you have managed to retain some info from the old system so that your comparisons are based on evidence rather than just perception. Most people dont have much in the way of historical data to make a reasonably credible comparison

Reed_Richards

One of the most often-quoted pieces of hearsay you will hear about heat pumps is that they are "slow to give heat".  I've looked into this.

If you have underfloor heating then underfloor heating is indeed slow to give heat and needs to be on pretty much all the time.  It makes good economic sense to combine underfloor heating with a heat pump because you don't need to make the water as hot as you do for radiator-based heating systems and with a heat pump economy of operation is all about minimising the difference between the source temperature (outside air temperature for an ASHP) and the temperature of the water you are heating.  So even heat pump owners with underfloor heating will confidently assert that heat pumps are slow to give heat when the truth of the matter is that they cannot really tell one way or the other.

On to radiator-based systems (which is what I have).  Hot water is hot water however it is heated and when your radiators are at the hot water temperature at which they were specified to operate then the heat you get is entirely down to the radiators.  The total heat output of my new radiators at their design temperature of delta T = 27.5 C is 9.7 kW.  I did an estimate for the output of the old radiators used with my oil boiler assuming delta T = 50 C and it is 12.7 kW.  That's very significantly more so once at temperature they would have heated my house faster.  My new radiators are supposedly "right-sized" to meet the heat requirement of my house (actually about 9% over).  The justification for not getting radiators with even greater output is that this will cause the heat pump to cycle.  With hindsight I believe that that is baloney, most of the time the outside temperature is hotter than your radiators were sized for so most of the time your heat pump will cycle anyway.  So one lesson I can pass-on is that if you want a house you can heat quickly, over-size the radiators.  That applies whatever your source of heat is.

The other aspect of speed of heating is how long it takes to get the radiators from cold up to their operating temperature.  I replaced a 24 kW oil boiler with a 12 kW heat pump so the oil boiler could heat the water twice as fast.  But it needs to get the output water from 10 C (say) to 85 C whereas the heat pump only need to get to 50 C so in principle it evens out.   Unfortunately I have no data for my oil boiler with which I could make a direct comparison.  So this is the aspect of speed of heating I am least confident about.       

Martyn1981

Here's a fun question that someone with a better mind than mine, may be able to advise on.

I was chatting with my sister yesterday, and she's finally able to make some moves on the ASHP and PV. Things were held up for months due to delays getting 3phase installed. The DNO was great, but they needed the energy company on site to change the meter, and that's where things fell down.

But, 3phase in, and my sister explained how the work was delayed as the drills they had (or drill bits) weren't long enough to get through the walls. She also complained how those same walls, being from the original build, around 140yrs ago, and solid, had meant extra expense with IWI to make them compatible with the ASHP.

That all got me thinking, and yes that's the dangerous part!

So, the house has been extended backwards, and to the side, over the years, so these thick solid walls only make up part of one side, and part of the front now. The original rear, and one side, are now internal walls.

Thinking back to many of Zeupater's comments about the benefits of a thermal store, and also thermal mass, to help stabilise temperatures, I started to do some maths, and based on an 18 inch wall, that's 20ft across, roughly 20ft tall, and 30ft to the side, I came up with 1,500ft3, and for calculation purposes, a 15kg concrete block being 0.375ft3, so a total of roughly 60tonnes.
I'm guessing that the stone is denser, so perhaps closer to 100tonnes of thermal mass inside the house, which will help to stabilise temps?

Obviously, the 'normal' single skin internal walls, will all help, but I think my sister should look upon those original walls as a long term benefit too, not just an expensive hassle during the upgrade?


Just a side note, and commenting under the 'bleeding obvious' heading, but when they moved into the property in late 2019, its various extensions over the 140yrs, meant it was almost two properties, with two sets of bathrooms, kitchens and heating systems, both having their own separate oil boilers. After the renovation, and importantly, massive amounts of insulation, and to get it ready for a single ASHP, the plumbing was combined into one system, and one of the diesel burners was removed. Yet the property temps were fine through our recent cold winter.

1st rule - Insulate, insulate, insulate!