Optimising a heat pump

matelodave

FreeBear said:

matelodave said: Taking the car analogy a bit further, I know that if I carefully drive at around 50mph everywhere and avoid heavy braking and acceleration I can get around 65mpg but I dont normally do that (as it boring)  and so only get around 55 (2litre automatic diesel AWD).

Same. Drive carefully would get over 50mpg. Go flat out round a race track, and only get 25mpg (1400cc Alpine engine with twin Dellorto side draughts). Good fun...

  

70sbudgie

TroubledTarts said:

70sbudgie said:

I've been quoted a design scop of 3.8. Have I done the salesman a disservice by not believing him when he said how good that was? If the standard target is 3. What is the likelihood I would achieve the design scop? (Or higher?) I am willing to read the manual and tweak.

Any plans on adding a battery to your setup?

What tariff have you got your eyes on?

These are loaded questions as they will determine how far your can push the scop of that's your aim or just how cheaply you want your heating with may mean a reduce cop working around peak time loaded smart tariffs.

The SCOP of 3.8 goes with a design temp of 47° at outside temp of -3.8°.

The design only requires me to change 2 radiators, but the salesman went to great pains to tell me that their price is fixed for a HP and 10 radiators. (Before the survey) 

What I am trying to work out is if I can identify some additional radiators to upsize, can I bring that 47° down? I haven't yet had a chance to get sufficiently proficient at Heat Punk to work it out for myself and strangely the installer is not keen to help me identify any additional radiators to change or share their design with me. (Edit to add that the design has now appeared.)

I am currently on Agile, with an EV and PV. I have been eyeing up a battery, but can't decide what size to go for. An HP would impact that decision.

I also have another half who considers all my energy savings as my hobby, so has limited patience for (helping to) fund it.

FreeBear

70sbudgie said: What I am trying to work out is if I can identify some additional radiators to upsize, can I bring that 47° down?

If you can run your current heating system at say 40°C, see which rooms won't get up to temperature.

Running my system at 40°C, I have three rooms that struggle to get to target (bathroom, kitchen, and a north facing dining room). Kitchen is already maxed out on radiator, so unless I install a second plinth heater, not much more I can do. The bathroom would need additional studs inserted in to a lath & plaster wall to take the weight of a bigger radiator. The dining room would benefit from extra insulation, but at least I have wall space to fit a bigger radiator or even a second one.

Your salesman/surveyor is probably tied to using MCS guidelines, so if you were wanting bigger radiators in a bedroom, you may need to convince him that the space is a study or lounge (higher target temperature). Alternatively, replace with upsized ones once the installation has been completed.

Reed_Richards

If you have a design it should tell you the heat loss from each room, the heat output from the radiators in that room (at the design temperatures) and the ratio.  You need the ratio to be greater than 1 (or 100%) for the room to be warm enough at the design outside temperature.  The rooms with the smallest ratio are the ones with the greatest need of larger radiators.  I went through three iterations before we agreed on a final set of radiators for my design (and with hindsight there was still room for improvement).  

70sbudgie

It sounds a little cynical, but having "sold" me a unit price (I've not signed anything yet), with 2 additional radiators, and then the survey identified that only 2 needed changing, they must be very pleased that their fixed price means I'm paying for 10 radiator changes. So I'm a bit loathe to change radiators afterwards, when this installer will do it for no extra cost - as long as I can persuade them to actually change the extra radiators that they include in their fixed price. 

But all is good, because Heat Punk gives me the opportunity to replicate their calcs for myself, now I have a copy of the design.

FreeBear

When I had a quote from Octopus last year, I was assured that the price may come down after the survey if some/all the radiators were already of a sufficient size.

Reed_Richards

But it's more fun to see if you can upsize the radiators to reduce the operating temperature.  If you can't then negotiate for a price reduction.

NedS

Reed_Richards said:

But it's more fun to see if you can upsize the radiators to reduce the operating temperature.  If you can't then negotiate for a price reduction.

Yes, we were lucky that when we had our system designed under the ECO4 scheme, the installers were happy to replace all the radiators, so we pretty much went with the largest rads we were able to accommodate in each room, which when cross-referenced with the room by room heat losses resulted in a well balanced system. We had one main living room that was hard to heat so we added an additional 2000x600mm radiator to the existing 1600x600 rad.

Anyway, the upshot is that we are running 32C flow temps, only increasing to 34-35C on very cold days, but with average ambient temps of 3-5C, we are just right at 32C flow temps for 19C indoor temps. As a result, efficiency is good and running costs are significantly lower than our previous oil boiler (or gas).

My advice - maximise the size of your emitters to minimise the flow temps.

stripling

@70sbudgie
What I am trying to work out is if I can identify some additional radiators to upsize, can I bring that 47° down? I haven't yet had a chance to get sufficiently proficient at Heat Punk to work it out for myself and strangely the installer is not keen to help me identify any additional radiators to change or share their design with me.

I did exactly this with an 🐙 installation. I used a  conversion calculator  and followed the heat geek quick method for a Delta T of 20 but I was also given an interactive spread sheet to calculate rad sizes from scratch and good support in the Renewable Heating hub and used Heat Punk.  My house has 'irregular' insulation so 🐙 accepted that a basic heat loss assessment wouldn't cut it and agreed to increase some rad sizes.

The key issues for good low flow running imo are 1) water volume; 2) good pump sizing with a wee bit of head room; 3) pure weather compensation - by cutting out room thermostats.  

My 6kw Daikin system was designed to run at the bog standard 🐙 50º but using the above, runs very efficiently at 38/39º flow temps. I'm getting an approximate C.O.P. of more than 4 (tho' I'm more interested in energy consumption and smooth - as in no cycling - operation than COP/SCOP.)  

NedS

My general checklist, in no particular order:

1. Reduce unnecessary complexity in the design (buffers, LLH, multiple zones and TRVs all add complexity that potentially reduces performance). Try to keep the ASHP within 10m of the tank/plant to minimise the pipe run.

2. Maximise emitter size (try to increase radiator sizes to the maximum permitted by the available space. Use K2 and consider 700mm high replacements for more standard 600mm radiators etc to maximise the space). Smaller radiators = higher flow temps = higher running costs.

3. Maximise the system volume. Maximising radiator sizes will help, as will a volumiser tank (not a buffer) on the return flow and using 28mm/22mm pipework throughout (copper pipes within the heated envelope of the house are also emitters if they are not insulated - see point 2). A large volume, and hence large thermal mass, really helps in winter with defrost cycles and cycling. Aim for a system volume maybe 4 times the recommended minimum (e.g, 200L for a 50L recommended minimum). Run a single zone with no TRVs (or all fully open) to maximise the available volume.

4. Pay attention to flow rates, they need to be significantly higher than for gas boilers (typically 20-30L/min). Large pipe sizes help and also help increase volume (point 3).

5. Run with weather compensation - automatically adjusts the flow temps to match the outside ambient temperature.

6. Don't undersize the heat pump - thrashing your heat pump to death when it's -5C outside to try to stay warm isn't going to help it's performance.

7. Site the ASHP in a south facing sunny location if you are able as the air may be a degree or two warmer which can make a big difference over the year.

8. Switch to a tariff with cheaper rate electricity, especially in winter, as you'll be using a lot of it. Solar panels in summer can offset running costs in winter.