I bought a Heat Pump

Reed_Richards

In December I posted that my heat pump had used 6930 kWh of electricity in it's first year of use.  My energy consumption from 31st March 2021 to 31st March 2022 has been 5330 kWh.  That's quite a big drop! 

I would like to believe that the main contributing factor is my getting to grips with Weather Compensation after a few months and thereafter using less conservative parameters than had been set by the installer.  But we have also generally had a milder winter than last year.    

akwexavante

The video is tense for me and hard to watch because of the unnecessary background noise (sorry Music), distracting, frustrating, not needed and doing the video a huge disfavour.    Please do it again but with no background music, it's just not needed at all.

Reed_Richards

akwexavante said:

The video is tense for me and hard to watch ...

Nothing to do with me, squire.  Just a video that somebody trawled out of the internet (which I don't particularly agree with).  

Martyn1981

Looking for thoughts (and looking at you RR and Shiny ) and advice on something I've been pondering. And that's high(er) water temp ASHP's. I've seen these touted in the news a few months back as a solution, though it seems to me that 'normal' HP's can work for most, as explained to us on here.

So, my circumstances. Our GCH + DHW is down now to about 6,000kWh's pa, might be 5,000 this year with the mild start. We have a biggish boiler a 28CDi, but since install the house has been improved massively (DG, CWi, underfloor insulation, unheated porch and side 'garage', etc).

Our biggest HP problem though seems to be that we have microbore to each rad, most of which, for info, have over the years been upgraded to double panels/fins. So I understand that's a no-no full stop ...... but, it occurred to me that we have the rad temp on the boiler close to min - Let's say the dial goes from 8o'clock to 4o'clock, we have it on about 9. But I don't know how much that dial changes the temp, if it's just a small difference? When tested I noticed at 12 the rads were almost too hot to touch. The recent mild winter only needed the GCH on for about 2hrs twice per day, and I'd estimate that 6-8hrs per day would be the max at the coldest extended periods we've had in the past.

So, question one, would a higher temp HP possibly manage without having to change all the microbore to 15mm?

Question two is the most important though. Obviously at a higher temp the COP drops off, so do the higher temp units always operate at a higher temp, or only when needed? Could they have similar COP's to a 'normal' HP when heating needs can be met at lower temps?

I'm in no rush, so hoping to watch the technology, options and prices develop*, so don't want anyone to waste time helping if busy, but would be interested in general thoughts.

Many thanks.

*Also, as I mentioned on another thread, Wales has a different planning permission rule to England, requiring PP if the unit will be sited within 3m of a neighbour. Since my property is 7m wide, there's no avoiding PP, which I'm sure would be fine, but why go through the hassle, since a national move towards greener heating may mean the Welsh requirement is amended.

Reed_Richards

Heat pumps are set-up to use a much smaller temperature differential between the input and output of the radiators, typically the target is 5 C.  I don't know for sure but I think the reason they do this is purely to improve the heat output from the radiators.  So if, for example, I have 50 C in and 45 C out then the average radiator temperature is 47.5 C whereas if you had 50 C in and 30 C out the average radiator temperature would be 40 C and increasing from 40 C to 47.5 C makes a big difference to the radiator heat output.

In order to achieve the smaller temperature differential they use higher water flow rates than in "normal" central heating systems; I suppose the flow rate has to be 4 times greater to change the differential from 20 C to 5 C.  I think the reason that microbore pipes are a "no-no" is that they cannot sustain these higher flow rates.   But if you think it through you can still achieve an average 47.5 C by supplying water at 57.5 C and having a temperature differential of 20 C.  So I reckon that yes, in principle you could have a high temperature heat pump, one capable of 55 to 60 C output and keep your microbore pipes.

But would you want to?  Heat pumps that are capable of higher output flow temperatures don't achieve this without cost.  The efficiency of a heat pump is very dependent on the temperature differential between the outside temperature and the leaving water temperature.  Your (hypothetical) heat pump is always going to be targeting a leaving water temperature that is 7.5 C higher than mine (which works to a maximum of 50 C) so your efficiency and CoP will always be less than I achieve.  Given current heating costs it might be better to bite the bullet and replace those microbore pipes.        
      

2nd_time_buyer

In case this of interest to anyone. Here is the response from the Department for Business, Energy & Industrial Strategy on my lobbying for air-to-air heat pumps to receive grants and VAT free status (they have gone with the VAT free status but not grants).

They have based the lack of grants on the fact that air-to-air heat pumps do not provide hot water so the combined (heating plus hot water) efficiency is lower than an air-to-water system. Any thoughts?

One thing I noted was that the SCOP ratings for an A+++ air-to-air unit can be much much higher than quoted (e.g. 5.1 compared to 3.5).

Martyn1981

One thing that jumps out at me is this sentence in para 2 - "Reducing greenhouse gas emissions to net zero will require virtually all heat in buildings to be decarbonised and action is needed now to keep us on track to meet that requirement".

and partially backed up by the statement in para 4 - "But in some instances air to air heat pumps were more optimal, namely in smaller properties with low heat demand."

So they seem to recognise that there's not a singular HP solution, they also recognise the need to act asap, but then seem to decide the issue purely on the DHW issue. DHW can still be low carbon leccy, just from an immersion heater, or even a HPWH (heat pump water heater), and is a smaller annual demand than heat for properties.

shinytop

Martyn1981 said:

Looking for thoughts (and looking at you RR and Shiny ) and advice on something I've been pondering. And that's high(er) water temp ASHP's. I've seen these touted in the news a few months back as a solution, though it seems to me that 'normal' HP's can work for most, as explained to us on here.

So, my circumstances. Our GCH + DHW is down now to about 6,000kWh's pa, might be 5,000 this year with the mild start. We have a biggish boiler a 28CDi, but since install the house has been improved massively (DG, CWi, underfloor insulation, unheated porch and side 'garage', etc).

Our biggest HP problem though seems to be that we have microbore to each rad, most of which, for info, have over the years been upgraded to double panels/fins. So I understand that's a no-no full stop ...... but, it occurred to me that we have the rad temp on the boiler close to min - Let's say the dial goes from 8o'clock to 4o'clock, we have it on about 9. But I don't know how much that dial changes the temp, if it's just a small difference? When tested I noticed at 12 the rads were almost too hot to touch. The recent mild winter only needed the GCH on for about 2hrs twice per day, and I'd estimate that 6-8hrs per day would be the max at the coldest extended periods we've had in the past.

So, question one, would a higher temp HP possibly manage without having to change all the microbore to 15mm?

Question two is the most important though. Obviously at a higher temp the COP drops off, so do the higher temp units always operate at a higher temp, or only when needed? Could they have similar COP's to a 'normal' HP when heating needs can be met at lower temps?

I'm in no rush, so hoping to watch the technology, options and prices develop*, so don't want anyone to waste time helping if busy, but would be interested in general thoughts.

Many thanks.

*Also, as I mentioned on another thread, Wales has a different planning permission rule to England, requiring PP if the unit will be sited within 3m of a neighbour. Since my property is 7m wide, there's no avoiding PP, which I'm sure would be fine, but why go through the hassle, since a national move towards greener heating may mean the Welsh requirement is amended.

I think the high temp ASHPs are optimised for high temps, i.e. they will produce at 60 degrees more efficiently than mine or R_R's but maybe not so at 40 degrees. But even with a high temp ASHP, COP will still be better at 40 than 60.  And they will operate at the lower temps if asked.

Although Microbore isn't ideal it's not a complete no-no and I've heard of people using itfor ASHPs .   A higher temperature and corresponding lower flow will help as R_R says.  If you google Daikin HT you'll find some figures for COPs and minimum flow rates. 

It might be worth investing in a thermometer to measure your rad temps; you can get aquarium ones from amazon for next to nothing that are surprisingly accurate. Even if you can't work out an accurate heat loss, you could work out roughly how long you'd have to have (say) 55 degree radiators on to match your max 6-8 hours at 70 degrees or whatever temp your radiators are.  

  

2nd_time_buyer

Thanks Martyn - very good points.

For most flats air to water heat pumps is not an option as there is nowhere to put the external unit.  However there are single unit air-to-air heat pumps which only have two 4-inch vent holes on the outside wall, that could be suitable with little affect on the external appearance. Particularly if the flats are currently heated with electric heaters they would offer significant cost/CO2 savings. 

As it stands, the current grants ae only available to those people who have £5k+ to spend on top of the grant which excludes a lot of people.  

Martyn1981

Great point about leccy heated flats. Instant reduction in annual leccy consumption. We've got two 3.5kW a/c units, so effectively have a hybrid system and with PV you help with costs and external leccy demand too.

Small tangent, but what about businesses or charities, where DHW is less important, such as shops, or social clubs, even churches, air-to-air would work well, and any reduction in cost might help tip the balance.