Heat Pumps: anyone have one/thought about it?

[dirtychinchilla]

The rate of heat loss will increase as the surrounding environment gets warmer, but it's not a huge water volume and not like you can't just insulate it more. Every cm of the installation should be insulated though; particularly the pipe run from outside to inside, which from what I've seen is often overlooked.

 

[shroomz]

Yeah it's definitely a thing. My loft has been insulated both in the floor and the roof itself, someone wanted to do belt and braces when they floored it. It hovers around 10C in winter.

I'm going to pop some extra insulation over the cylinder and any volumiser or anything else that will emit.

You're totally right for a cold loft it wouldn't be ideal and lead to additional losses from the hot water that need made up.

 

[shroomz]

The rate of heat loss will increase as the surrounding environment gets warmer, but it's not a huge water volume and not like you can't just insulate it more. Every cm of the installation should be insulated though; particularly the pipe run from outside to inside, which from what I've seen is often overlooked.

With decent insulation on the piping too, not just crappy grey 10mm lagging you get for pennies. I think there's a brand called primary pro that's quite rigid and seems to be the gold standard.

 

[Nutty667]

Why? They're insulated.

No insulation is perfect. The colder the ambient temp around the cylinder the more heat loss there will be, pulling down efficiency. That's why traditionally hot water cylinders were usually in the airing cupboard not in the loft like the cold water tank.

 

[dlockers]

No insulation is perfect. The colder the ambient temp around the cylinder the more heat loss there will be, pulling down efficiency. That's why traditionally hot water cylinders were usually in the airing cupboard not in the loft like the cold water tank.

I'm not disagreeing with the logic but you must be in fractions of a percentage of efficiency.

Old vented cylinders aren't comparable at all imo. They used to lose loads of heat and hence airing cupboards were quite useful places to warm towels etc. with the waste.

My unvented is cold to the touch it's so well insulated. On holiday when I used no hot water it used 3kwh to maintain 60 degrees.

 

[PermaChanged]

My unvented is cold to the touch it's so well insulated. On holiday when I used no hot water it used 3kwh to maintain 60 degrees.

Oooooo, can we get in to conversations as to why you shouldn't be maintaining at 60c, given it's a huge waste of electricity?

 

[SpeedFreak]

Set at 52-55 and basically don't worry. My new cylinder is in a cold loft. Everything is lagged to the maximum and the cylinder won't lose much heat there. All running off a 5kw ASHP.

 

[PermaChanged]

I think ours is stored at / topped up to 48c with a recharge when it drops to 42c - pretty sure the Mrs showers at 42c so it's purely provided by the cylinder haha.

We do have a fortnightly anti legionnaires cycle, but due to the low temperature storage we have a large percentage of turnover of the cylinder.

 

[shroomz]

Good to know the modern insulation on modern unvented cylinders is now good. Only £25 for an extra jacket so I might get that anyway and chuck it over the other bits in the plant room that might not be so well insulated.
Depends if I need to, which I'll only know in winter so no rush

 

[bigmike20vt]

My unvented is cold to the touch it's so well insulated. On holiday when I used no hot water it used 3kwh to maintain 60 degrees.

out of curiosity how long was your holiday?

60 degrees being a little on the warm side aside (iirc 50 degrees is enough to sort out anything nasty and will waste less energy)... however if it was a week holiday, i would say 3kwh loss over a week is not so bad, esp not if it was heated using cheap off peak energy for instance...... even my house battery will lose some charge and then there is the inefficiency of charging it.

obviously wasted energy is bad, however to play devils advocate if that "wasted" energy ultimately comes from clean off peak energy it is not so bad imo.... and also on top of that a tiny amount of lost heat into your attic in winter may not be all bad anyway.

 

[jpaul]

or whether it was a winter/ski holiday - our loft must have been mid-20's recently.
having 60c to support overall volume of mixed down hot water doesn't sound unreasonable.

Are labour maintaining green hp subsidy

 

[bigmike20vt]

Are labour maintaining green hp subsidy

I think we will get shouted at if we goo to political outside of speakers corner.......... however i really hope so. It is one of the few things the current lot have done which I genuinely applaud. (even though it wont benefit me as I am not ripping out a perfectly good fairly new boiler and i doubt it will still be in place in 5 - 10 years time)

 

[b0rn2sk8]

Mixing down is a waste of energy.

You are literally paying to heat water to 60c and then cool it down to ~38-40 to use it.

Our hot water store only gets heated to 47C. The only reason to go hotter is if you need to store more energy (e.g. to last all day for cheap overnight time of use pricing) or to do a legionella cycle. The irony is that the lower temperature you store at, the more water you cycle through the store and the lower the risk of legionella.

If you are heating on gas, there is no time of use pricing so you might as well heat to a lower temperature. It’s more efficient to heat and the cylinder has a lower heat loss.

 

[jpaul]

shower about 10L/min for 6-7mins so maybe use 40L of 60C water, so a 200L tank is 5 showers, kitchen use too, and if god forbid someones wants a bath, then maybe half the tank has gone.

when the gas boiler (like dlockers) is on heating tank, ideally want it done in one shot at most efficient/powerful mode (condensing/modulation of little use anyway) -
if it's a hp want to store at temp efficient for that.

 

[b0rn2sk8]

the energy saved from heating a cylinder in one go using a gas boiler (e.g. no time of use pricing) is completely decimated by mixing down.

I’d need to calculate the numbers but I think you’d be wasting around 1/3 of the energy by mixing down 60C to 40C (when compared to 50C).

Edit: it uses 58wh to heat 1L of water from 10C to 60c, and only 45wh to heat to 50c, so yeh about 1/3 more energy.

 

[bigmike20vt]

shower about 10L/min for 6-7mins so maybe use 40L of 60C water, so a 200L tank is 5 showers, kitchen use too, and if god forbid someones wants a bath, then maybe half the tank has gone.

when the gas boiler (like dlockers) is on heating tank, ideally want it done in one shot at most efficient/powerful mode (condensing/modulation of little use anyway) -
if it's a hp want to store at temp efficient for that.

i guess it depends on your house size but for us, a house of 2 adults and 1 kid, i think capacity for 4 shower and some kitchen use is actually a decent amount.

As for the bath......... i wont lie i love a good soak as much as the next person, however if your goal is efficiency then baths are a bit of a none starter. I am not saying never have one (though if i had my way next time we redo the bathroom i would get rid of ours) but just that they are probably not something we should be having daily IF you want to reduce consumption.... and i would not spec a heating system around having one as a treat.

 

[bigmike20vt]

the energy saved from heating a cylinder in one go using a gas boiler (e.g. no time of use pricing) is completely decimated by mixing down.

I’d need to calculate the numbers but I think you’d be wasting around 1/3 of the energy by mixing down 60C to 40C (when compared to 50C).

Edit: it uses 58wh to heat 1L of water from 10C to 60c, and only 45wh to heat to 50c, so yeh about 1/3 more energy.

not disagreeing with you but to play devils advocate 1l of 60 degree water will however create more than 1l of 50 degree water when mixed down to say37 degrees. There will be loss for sure but not 1/3.

 

[b0rn2sk8]

not disagreeing with you but to play devils advocate 1l of 60 degree water will however create more than 1l of 37 degree water when mixed down. There will be loss for sure but not 1/3.

Yes, good point, that was a bit dumb of me. Still, there are losses….

 

[PermaChanged]

Cylinder size plays a crucial part of temperature storage requirements too, for effectively meeting the needs of the user.

If you've only got a 150l cylinder, but want a 300 litre bath of 38+c water then storing between 45c to 50c is a dumb move. We ended up with a 300l cylinder, which means storing at those mid to high 40s is feasible for our use case.

As mentioned previously, we heat to ~48c and recharge when the temperature drops to ~42c based on the internal thermometers - that 6c recharge takes ~30 mins and we recharge twice within a 24hr period.

We could go for uber efficiency and choose to never recharge between certain hours, I can't imagine we'd drop temps particularly quickly from 42c to below comfortable shower temps given heat loss reduces more and more the smaller the temperature differential.