Heat Pumps: anyone have one/thought about it?

There are more effective ways of adding system volume with the pipes being outside the thermal envelope of the house though as they’ll increase the heat loss.

It’s also one of those things where once you have enough, adding more doesn’t make it better and in fact it starts having a negative impact. There is a balance to be struck.

For example, the bigger the volume, the longer the heat pump has to run and the more energy is consumed getting the water in the loop up before up to temperature and start delivering the target power level to the property. They modulate their pump speed to maintain the target delta T (5C) between the flow and the return.

This is another reason why you don’t really want to turn them off unless you have time of use electricity where you can lower the average cost of the input to more than make up for the reduced performance.
 
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Long outside pipe runs probably aren't beneficial because of the losses from heating pipes being outside, regardless of how well insulated they might be. Extra system volume from longer runs inside then probably aren't too bad though, but long runs hurt system response.

The video on system volume didn't make complete sense to me on the defrosting either. More volume can improve defrost speed because average water temperature is higher when the heat pump is reversed, but the time between defrosts won't be improved because the same amount of energy has to be put back into the system regardless. The system refreezes mostly based on system load (and outdoor weather conditions, which you can't control anyway!), so the recovery after defrosting and the time to the next defrost won't really be effected by system volume.
 
b0rn2sk8 said:
The installer will give you an estimated energy use based on a typical year in the U.K. based on the MCS formula.

You can’t fit a pump to an unvented cylinder, they operate at mains pressure so it doesn’t need it anyway. There isn’t a material pressure loss going from first to second floor unless your plumbing is stupid.

MCS guidelines dictate how big the cylinder should be, it’s based on number of bedrooms. https://mcscertified.com/wp-content/uploads/2019/08/Domestic_HW_cyl_selection_guide.pdf

How much hot water you actually use depends on the temperature of the cylinder, the hotter it is, the more energy it contains. Typical shower temperature is 37-39C, typical incoming cold water temperature is above 10C so you are mixing 50c water down to 38 with 10C water 1L out the shower is well below 1L out the tank.

Your temperature probe is at the bottom of the cylinder, the water at the top of the tank is more like 55C.
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It looks like we'd have to have a 210 litre cylinder then going by that. It depends on what heat pump size they suggest I guess. I'm hoping our heat loss is pretty low and we can have the smaller Daikin. I suspect we'll get a large increase in the heat loss calc due to our wood burner and vents in the living room for it. As long as it's not so high that we have to use the 9kW (aka larger downrated unit). I'm guessing with only 7100kWh usage of gas per year our heat loss should be pretty low overall though.

I saw the YouTube video of Nicolas Raimo's install with the Cosy 6 and the COP figures look pretty poor to me. I don't particularly like the look of the Cosy 6 either so would certainly like to avoid that.
 
DarkBahamut said:
Long outside pipe runs probably aren't beneficial because of the losses from heating pipes being outside, regardless of how well insulated they might be. Extra system volume from longer runs inside then probably aren't too bad though, but long runs hurt system response.

The video on system volume didn't make complete sense to me on the defrosting either. More volume can improve defrost speed because average water temperature is higher when the heat pump is reversed, but the time between defrosts won't be improved because the same amount of energy has to be put back into the system regardless. The system refreezes mostly based on system load (and outdoor weather conditions, which you can't control anyway!), so the recovery after defrosting and the time to the next defrost won't really be effected by system volume.
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Agreed. It’s all about the energy being put in, the temperature of the fin stack and the humidity. As soon as the fin stack hits negative and humidity is high, you’ll start getting freezing.

In my experience, it’s the days that have lots of mist/fog which are the worst for defrosts. It’s all the wet and and humidity pulled through the radiator on the back.

The days last week where it was cold and sunny, we didn’t get any defrosts, the one day that was a similar temperature but overcast and thick fog all day, we were defrosting every 40 mins or so. It’s one day where cop was pretty bad but I’ve had plenty of good days to more than make up for it. The cold properly crisp days are not anything like as bad.
 
reef said:
I saw the YouTube video of Nicolas Raimo's install with the Cosy 6 and the COP figures look pretty poor to me. I don't particularly like the look of the Cosy 6 either so would certainly like to avoid that.
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I’m not convinced that install has the most optimal design but I think that was largely driven by customer choice, the limited offering from Octopus and circumstance.

For example the Daikin is much more controllable and can be tweaked more to the environment than the Cosy which he decided to have.

The combination of a very very long primary pipe run, the heat pump is quite small so it’s ability to deal with the volume is more difficult, micro bore pipe restricts flow which makes it harder to deal with the volume and the relativly low heat loss makes it a more challenging install. A heat geek doing a more bespoke design may have been able to get a bit more out of it.

The COP numbers are not great but I seem to recall it does the ‘time of use’ approach like I do which reduces both COP and cost. He more than makes up for it with solar and batteries but that shouldn’t be the method to make the costs work.
 
b0rn2sk8 said:
Agreed. It’s all about the energy being put in, the temperature of the fin stack and the humidity. As soon as the fin stack hits negative and humidity is high, you’ll start getting freezing.

In my experience, it’s the days that have lots of mist/fog which are the worst for defrosts. It’s all the wet and and humidity pulled through the radiator on the back.

The days last week where it was cold and sunny, we didn’t get any defrosts, the one day that was a similar temperature but overcast and thick fog all day, we were defrosting every 40 mins or so. It’s one day where cop was pretty bad but I’ve had plenty of good days to more than make up for it. The cold properly crisp days are not anything like as bad.
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We definitely had some serious defrosting in the fog too. You can see on the power graphs pretty much when the fog started and finished from the rather rapid increase in power spikes for defrosting! It was about 3-4x normal compared to the prior clear night at the same outdoor temperature (-5 C). We're A2A based so no proper COP readings for us, but it is possible to make some estimates based on heat loss calcs and known heating requirements from when we were using gas.

Heat pumps are a no brainer for any with solar & batteries though. The very coldest winter days are frequently also clear weather days, so you generate reasonably well on the days you need it most, plus you can load batteries on the cheap overnight. For the 5 days of the cold snap our total household electricity spend was under £12.
 
b0rn2sk8 said:
I’m not convinced that install has the most optimal design but I think that was largely driven by customer choice, the limited offering from Octopus and circumstance.

For example the Daikin is much more controllable and can be tweaked more to the environment than the Cosy which he decided to have.

The combination of a very very long primary pipe run, the heat pump is quite small so it’s ability to deal with the volume is more difficult, micro bore pipe restricts flow which makes it harder to deal with the volume and the relativly low heat loss makes it a more challenging install. A heat geek doing a more bespoke design may have been able to get a bit more out of it.

The COP numbers are not great but I seem to recall it does the ‘time of use’ approach like I do which reduces both COP and cost. He more than makes up for it with solar and batteries but that shouldn’t be the method to make the costs work.
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In the location I hope to position the heat pump, it is approximately 4.5-4.8m of outside piping, with around 8m or so in the loft which should remain slightly warmer. It's actually next to our Mitsubishi inverter for our split air con and that works very well there for heating without any issues.

Anyway, the wife seems to have no objections so I'll be going ahead with it tomorrow hopefully.
 
Ron-ski said:
Longer main heat pump feed and return pipes could actually be beneficial as it increases system capacity, upsidedownfork did a video about it very recently on YouTube.

I'm in the process of booking a survey with a local installer.
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As well as @b0rn2sk8’s note, this is a problem for the DHW loop. You want your volume to be in the heating circuit rather than in the DHW circuit. My run to the cylinder is quite long so I have to heat all the water in the pipes up to a high temp to heat the cylinder. Most of the DHW run is in the loft so heat loss is no benefit to the rest of the house (similarly to having a long external run).
 
reef said:
In the location I hope to position the heat pump, it is approximately 4.5-4.8m of outside piping, with around 8m or so in the loft which should remain slightly warmer. It's actually next to our Mitsubishi inverter for our split air con and that works very well there for heating without any issues.
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Its not dissimilar to mine, I'm about 7m external and 12m in the loft - that's flow and return so half that for the single pipe run.
 
b0rn2sk8 said:
I’m not convinced that install has the most optimal design but I think that was largely driven by customer choice, the limited offering from Octopus and circumstance.
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Octopus seem happy with high flow temperature designs too (not sure if that applies for this one) and say that’s fine. I’m not convinced.
 
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50C isn't high but it is the top of what is considered low temperature. It is in my view, as high as you can realistically go for a minimum viable install which matches has gas running costs.

I think it will end up being the reality of most retrofits as going lower increases costs as others have found when getting quotes for systems designed at a lower temperature elsewhere. As with everything there is always a balance to be struck between getting the best performance and targeting good value.
 
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is it likely that eon are doing the same deal as ocotpus? im currently on eon next. they just mention £350 discount for current customers and dont give you an online quote, just to book a consultation.
 
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