The move to heat pumps

Dave_Fowler

Reed_Richards said:

QrizB said:A

ll other things being equal* it would be better to heat 1000 litres of water to 40C rather than 500 litres to 70C that you blend down:

  Anybody know any tricks for easy destratification?  

Most vented DHW systems have a pipe from the cold water storage tank which goes to the bottom of the hot water cylinder.  There will also be a hot water take-off pipe from the top of the cylinder, which supplies hot water to the house.  It also goes up to an expansion pipe in the loft.

Connect a 'central heating type' pump (with a non-return valve) between the two pipes so that the hot water from the top of the tank is pumped down to the tank's cold water inlet.  The pump motor is connected across the immersion thermostat, so that when the thermostat opens at the set temperature, the pump is activated.

I've had this system operating for many years.

Dave F

JKenH

michaels said:

JKenH said:

michaels said:

Martyn1981 said:

QrizB said:

Martyn1981 said:

JKenH said:

Why not just use an immersion heater for the DHW element using either a solar diverter or cheap overnight electricity? If the daytime rate is 14p and night time 5p you have the same savings as a COP of 2.8 and no loss of heat in the pipe work transferring the water from the heat pump to the tank (and back again). You can then run your heat pump at lower temperatures. 

Yeah, I was wondering that too, but I wasn't sure if you could get a tank big enough, and how much the power would have to be to heat that much water in just 7hrs in the winter.

The power required is pretty easy to work out.

A cubic metre of water weighs a tonne. The specific heat capacity of water is 4.2 joules per gram per degree C, 4.2 megajoules per tonne per degree C. If the water starts at 10 deg. C and is heated to 70 deg. C that's a temperature rise of 60 degrees and an energy requirement of 252 MJ.

A kilowatt-hour is 3.6 MJ, so heating the water will take 70 kWh. To heat it in 7 hours will require a 10kW immersion heater. Big by domestic standards (and drawing ~42 amps), but no larger than some modern instantaneous showers.

Thanks, cool (pun intended) numbers for me to play with.

From there, can I assume it's safe to half that number for baths and showers, on the basis that the water temp will be closer to 40C(?), so a mix, for example, of 10C cold feed and 70C from the tank?
So, for those 12 baths and showers per day it would take 35kWh, which I think ties in with the number he posted a long time back of DHW gas consumption being around 12MWh pa ...... if my memory serves me correctly.
So just need a 500lt hot water tank.

Starting to think that a heat pump, and one bath/shower per person per day, would be a lot more easy, affordable, green and sustainable.

It would help this conversation if we were able to come up with gas and electricity prices that would apply if they also reflected their environmental (Co2) costs.  Can anyone take a stab at this?

And then how would you treat oil CH? People living in the sticks are already paying a premium to heat their homes because the infrastructure isn’t in place to supply them with gas so do you then penalise them further? Should everyone not pay the same price for energy irrespective of where they live and how they heat their homes?

I have no problem with taxing oil and gas so everyone pays the same price per kWh equivalent as electricity to heat their homes but I suspect the electorate might see it differently.

Hopefully not causing too much offence, but if we want to get serious about climate change then we need to price energy use accordingly.  If we then decide we ant to offer subsidy to certain groups then that is fine but even those with no main gas we want to be facing the correct relative prices so they can make good decisions on the choice between better insulation and less energy use.

For example if oil prices were doubled to reflect the environmental cost but you were then compensated in cash for the increase in fuel bills I bet you would look for ways to save on the fuel bills and pocket the savings rather than just carry on using as much as you previously did.

I wouldn’t disagree with that but people using oil are in a minority and the real problem is that gas is so incredibly cheap that there isn’t any viable economic alternative. 

At least with oil, cheap rate electricity is on a par in cost terms and hence there are alternatives. I heat my water by electricity rather than oil. Space heating using my ASHPs (lounge and kitchen) is also on a par cost wise if one takes the average COP over the year, hence I only use oil CH when the rest of the house needs warming up. On a personal level if oil were to double in cost it would not be a big issue for me - if only the DNO would let me add more solar panels and a battery.

One only has to observe the comments on this board that gas is far and away the cheapest CH option (and  the externalities rarely feature in the recommendation). We could all heat our homes by electricity if we were so minded; after all half a dozen convector heaters would do the job at a capital cost of about £150 or oil filled radiators for about double the money. No real practical problem to making the switch overnight on an individual basis but the sting is the annual running cost. 

If the government whacked 100% VAT on gas there would be quite a public reaction.

As they say “it's the money not the principle“. 

Cardew

michaels  but if we want to get serious about climate change then we need to price energy use accordingly.

Depends who you mean by 'we'?

I suspect The 'man on the Clapham omnibus' and indeed the electorate won't see it that way, unless most of the world have a similarly strict policy on energy prices - and that includes China, India and the USA.

JKenH

michaels said:

Martyn1981 said:

QrizB said:

Martyn1981 said:

JKenH said:

Why not just use an immersion heater for the DHW element using either a solar diverter or cheap overnight electricity? If the daytime rate is 14p and night time 5p you have the same savings as a COP of 2.8 and no loss of heat in the pipe work transferring the water from the heat pump to the tank (and back again). You can then run your heat pump at lower temperatures. 

Yeah, I was wondering that too, but I wasn't sure if you could get a tank big enough, and how much the power would have to be to heat that much water in just 7hrs in the winter.

The power required is pretty easy to work out.

A cubic metre of water weighs a tonne. The specific heat capacity of water is 4.2 joules per gram per degree C, 4.2 megajoules per tonne per degree C. If the water starts at 10 deg. C and is heated to 70 deg. C that's a temperature rise of 60 degrees and an energy requirement of 252 MJ.

A kilowatt-hour is 3.6 MJ, so heating the water will take 70 kWh. To heat it in 7 hours will require a 10kW immersion heater. Big by domestic standards (and drawing ~42 amps), but no larger than some modern instantaneous showers.

Thanks, cool (pun intended) numbers for me to play with.

From there, can I assume it's safe to half that number for baths and showers, on the basis that the water temp will be closer to 40C(?), so a mix, for example, of 10C cold feed and 70C from the tank?
So, for those 12 baths and showers per day it would take 35kWh, which I think ties in with the number he posted a long time back of DHW gas consumption being around 12MWh pa ...... if my memory serves me correctly.
So just need a 500lt hot water tank.

Starting to think that a heat pump, and one bath/shower per person per day, would be a lot more easy, affordable, green and sustainable.

So to me the answer is to make high users (me) face the true economic (including environmental costs) in the marginal prices they face for gas and electricity and then they will be able to take sensible decisions on what heat source to use and how much heat altogether.

In theory the benefits system could be used to protect those on low and even middle incomes from the impact of this on their standard of living.  The slight problem being is that many are poor at budgeting and would not use an increase in benefits to meet increased energy costs nor understand how to limit usage to reflect the cost and would scream incredibly loudly about how the high energy costs were 'killing granny'.

It would help this conversation if we were able to come up with gas and electricity prices that would apply if they also reflected their environmental (Co2) costs.  Can anyone take a stab at this?

Energy suppliers are calling for changes to the levies on gas and electricity to reduce energy bills for their most vulnerable customers and decrease the cost of electrical heating.

The current cost of electricity is comprised on various environmental and social obligation costs such as the Renewables obligation, Feed-in Tariff and Smart Export Guarantee.  

Currently, these obligations account for 23% of the cost of electricity, something that energy suppliers say is unfair as gas costs currently only include less than 2% of environmental and social obligation costs. 

“Lumping social and environmental levies on to the electricity side of the bill means that gas – the main polluter in UK homes – effectively has its ‘thumb on the scale’ when it comes to the true cost of energy in the UK.

"Indeed, we now have the paradoxical situation that green electricity carries ten times more taxation than gas. Rebalancing the taxes between gas and electricity would leave the average dual fuel bill as it is today but would lead to energy costs falling as we increasingly electrify society.“

https://www.dyballassociates.co.uk/energy-suppliers-call-for-changes-to-electricity-and-gas-levies

Hexane

JKenH said:

michaels said:

Martyn1981 said:

QrizB said:

Martyn1981 said:

JKenH said:

Why not just use an immersion heater for the DHW element using either a solar diverter or cheap overnight electricity? If the daytime rate is 14p and night time 5p you have the same savings as a COP of 2.8 and no loss of heat in the pipe work transferring the water from the heat pump to the tank (and back again). You can then run your heat pump at lower temperatures. 

Yeah, I was wondering that too, but I wasn't sure if you could get a tank big enough, and how much the power would have to be to heat that much water in just 7hrs in the winter.

The power required is pretty easy to work out.

A cubic metre of water weighs a tonne. The specific heat capacity of water is 4.2 joules per gram per degree C, 4.2 megajoules per tonne per degree C. If the water starts at 10 deg. C and is heated to 70 deg. C that's a temperature rise of 60 degrees and an energy requirement of 252 MJ.

A kilowatt-hour is 3.6 MJ, so heating the water will take 70 kWh. To heat it in 7 hours will require a 10kW immersion heater. Big by domestic standards (and drawing ~42 amps), but no larger than some modern instantaneous showers.

Thanks, cool (pun intended) numbers for me to play with.

From there, can I assume it's safe to half that number for baths and showers, on the basis that the water temp will be closer to 40C(?), so a mix, for example, of 10C cold feed and 70C from the tank?
So, for those 12 baths and showers per day it would take 35kWh, which I think ties in with the number he posted a long time back of DHW gas consumption being around 12MWh pa ...... if my memory serves me correctly.
So just need a 500lt hot water tank.

Starting to think that a heat pump, and one bath/shower per person per day, would be a lot more easy, affordable, green and sustainable.

It would help this conversation if we were able to come up with gas and electricity prices that would apply if they also reflected their environmental (Co2) costs.  Can anyone take a stab at this?

Should everyone not pay the same price for energy irrespective of where they live and how they heat their homes?

No, they shouldn't.

JKenH

Hexane said:

JKenH said:

michaels said:

Martyn1981 said:

QrizB said:

Martyn1981 said:

JKenH said:

Why not just use an immersion heater for the DHW element using either a solar diverter or cheap overnight electricity? If the daytime rate is 14p and night time 5p you have the same savings as a COP of 2.8 and no loss of heat in the pipe work transferring the water from the heat pump to the tank (and back again). You can then run your heat pump at lower temperatures. 

Yeah, I was wondering that too, but I wasn't sure if you could get a tank big enough, and how much the power would have to be to heat that much water in just 7hrs in the winter.

The power required is pretty easy to work out.

A cubic metre of water weighs a tonne. The specific heat capacity of water is 4.2 joules per gram per degree C, 4.2 megajoules per tonne per degree C. If the water starts at 10 deg. C and is heated to 70 deg. C that's a temperature rise of 60 degrees and an energy requirement of 252 MJ.

A kilowatt-hour is 3.6 MJ, so heating the water will take 70 kWh. To heat it in 7 hours will require a 10kW immersion heater. Big by domestic standards (and drawing ~42 amps), but no larger than some modern instantaneous showers.

Thanks, cool (pun intended) numbers for me to play with.

From there, can I assume it's safe to half that number for baths and showers, on the basis that the water temp will be closer to 40C(?), so a mix, for example, of 10C cold feed and 70C from the tank?
So, for those 12 baths and showers per day it would take 35kWh, which I think ties in with the number he posted a long time back of DHW gas consumption being around 12MWh pa ...... if my memory serves me correctly.
So just need a 500lt hot water tank.

Starting to think that a heat pump, and one bath/shower per person per day, would be a lot more easy, affordable, green and sustainable.

It would help this conversation if we were able to come up with gas and electricity prices that would apply if they also reflected their environmental (Co2) costs.  Can anyone take a stab at this?

Should everyone not pay the same price for energy irrespective of where they live and how they heat their homes?

No, they shouldn't.

I can’t help being a good socialist 😉

Edit: seriously, though, virtually everyone (unless you live in an extremely remote location) has mains water, mains electricity, telephone/broadband etc so why not mains gas? There is a push to roll out broadband to those  few areas that do not have it, paid for by the rest of us so why deny some locations gas and effectively deny some people the opportunity to cook and heat their homes at the same cost as others. As you will see from the other link I have published electricity is effectively taxed at 10x the rate gas is to cover green initiatives. Some people do not have the choice and have to pay extra levies because they don’t have gas. There has never been the political will to make gas available nationally. You might say it is all a bit late now as gas is supposed to be in the way out but I suspect gas is still being laid out to new housing developments.

There are minor discrepancies regarding pricing of energy regionally but generally most utilities have reasonably consistent charging. There is a very good case to be made for Scottish electricity customers to pay significantly less than customers in the south of England as their electricity is so much cleaner but that is not politically viable.

It’s just a point of view.

silverwhistle

shinytop said:

 

But that's very low gas usage.  I know I go on about having to use less energy but I won't put up with 16c in the lounge ....

No, last year was high! But what's wrong with 16c in the lounge if you are not there? The woodburner gets it very warm very quickly. Funnily enough I used gas more in the spring when it was wet and windy (see MatelotDave's point), was feeling the cold and couldn't be bothered to light the fire. My kitchen doesn't even have any heating but I've never missed it as I'm active in there.  I'm certainly not the sort of lass who goes winter clubbing in Newcastle in not very much.. and I dress appropriately for skiing and such like.

Subsidising prices is never a good idea and there are plenty of examples around the world to demonstrate this. If you want to achieve a positive outcome encouraging consumption will not be a solution, although I'm not sure how best to achieve the change. Certainly we have seen how external stimulus has brought down the cost of PV and wind, so we'll undoubtedly need some carrots for HPs too.

On a visit this week to the plumbers merchant I noticed a poster on the wall for an on-line course in heat pumps, so maybe awareness is gradually seeping in. I wonder if the local tertiary colleges have started to gear up yet?

Reed_Richards

Dave_Fowler said:

Reed_Richards said:

QrizB said:A

ll other things being equal* it would be better to heat 1000 litres of water to 40C rather than 500 litres to 70C that you blend down:

  Anybody know any tricks for easy destratification?  

Most vented DHW systems have a pipe from the cold water storage tank which goes to the bottom of the hot water cylinder.  There will also be a hot water take-off pipe from the top of the cylinder, which supplies hot water to the house.  It also goes up to an expansion pipe in the loft.

Connect a 'central heating type' pump (with a non-return valve) between the two pipes so that the hot water from the top of the tank is pumped down to the tank's cold water inlet.  The pump motor is connected across the immersion thermostat, so that when the thermostat opens at the set temperature, the pump is activated.

I've had this system operating for many years.

Dave F

Thanks Dave F; that's very helpful.  I don't have an unvented system but there seems to be a spare port at the base of cylinder.  I would need a potable water pump which is very similar to 'central heating type' pump.

k_bagpuss

I’m about to have a full heat pump system into my house replacing the current gas boiler, actually getting rid of the gas supply now as we only had the gas in for the boiler anyway. It’s through a pilot scheme in the North East via E-On and Newcastle City Council so it’s 100% funded. Just need to agree to it being heavily monitored for the first 12 months. I like the green credentials, so I’m happy to give it a go

EVandPV

k_bagpuss said:

I’m about to have a full heat pump system into my house replacing the current gas boiler, actually getting rid of the gas supply now as we only had the gas in for the boiler anyway. It’s through a pilot scheme in the North East via E-On and Newcastle City Council so it’s 100% funded. Just need to agree to it being heavily monitored for the first 12 months. I like the green credentials, so I’m happy to give it a go

Wow, sounds like a great offer !
Do they pay your electricity costs for running the heat pump for the first year too ?