Confused: AWHP, NTHs, Biogas Heating?!!

Haveyougotenoughtime

Hi again,

So we have an old damp detached 2 bed house that we're renovating.
I'd like to use renewable energy to heat the water and space.

Would somebody be able to run through the pros and cons of the following options:

1. Air to water heat pumps
We're going to need a lot of heat in the winter - is this adequate - I've read that they don't give out too much heat in winter....

2. Plug in Night Storage Heaters
I know nothing about these - do they give off enough heat - I've read they tend to run out of heat in the evenings?
And I'm assuming this would have to be coupled with an immersion heater for the water?
Would we ever run out of hot water?

3. Biogas or biofuel...
Bear with me - I've just had a random conversation with someone who says that they use Biofuel/biogas or something as well as gas?

4. Any other options that I've not considered....
...really want to avoid solar....

Thanks!

Haveyougotenoughtime

5. Biomass boilers?

6. Ground Source Heat Pumps?

  

Gerry1

Presumably you have gas but want to go green and don't care how much more it costs?

Night storage heaters are viable, and if correctly dimensioned won't go cool in the evenings.  Clever ones such as Dimplex Quantum also have a built in convector so you can top up at expensive day rates if you've messed up.  They can run off 13A sockets but it's far better to run them on a separate E7 circuit that's automatically switched by the meter.  However, they are expensive to buy and expensive to run (but not as expensive as an electric boiler or panel heaters).

The immersion heater should run off a similar E7 switched circuit.  It also makes sense to have a 'Boost' immersion heater halfway up the tank on a 24h circuit and a local timer that will switch it off after a maximum of two hours.  Again, you use the Boost heater only if you've messed up and the water has gone cold before the E7 kicks in late in the evening.

Once again, any of this is far more expensive than gas, and will also make your property far less attractive to potential purchasers.

QrizB

I;m not a heating engineer but here's my take on heat pumps - ASHP and GSHP. Someone else can write abouth the other technologies (or I might come back after dinner).

Heat pumps move heat (energy) from A to B (typically from a colder place to a hotter place) making A colder and B hotter. You have to put energy into the pump to make it work. The heat that you get out of the system at B is the sum of the heat that you hanve put into the system plus the heat that you have taken from A, less any losses along the way (and there are always losses).

For an air source heat pump (ASHP), "A" is the air. Air mixes pretty well so you can get a lot of heat using a realtively small outdoor box with a big fan in it.

For a ground source heat pump (GSHP), "A" is the ground. Ground doesn't mix very well so you need to draw energy from a lot of it, which means either a paddock-sized array of pipes or some deep boreholes. Neither of these are likely to be options for a 2 up, 2 down renovation unless it's somewhere very special.

You can also choose whether you deliver the heat at "B" as hot water or hot air. Hot water lets you use the sort of plumbing people are used to, with radiators (or preferably underfloor heating) and a hot water tank. These are the systems the Government is encouraging with its RHI scheme. The downside is that these systems tend to be quite large and expensive; £10k for ASHP and £20k for GSHP are common guide costs. Hot air on the other hand is cheaper (maybe £3k for a small house) and potentially more efficient at heating, and give you the option of cooling (air con) in the summer, but won't give you a tank full of hot water. Air heaters aren't RHI-eligible for some reason (possibly to discourage domestic air con).

The efficiency of a heater is the ratio of the amount of heat (energy) you get of it, divided by the energy you put into the system. For a conventional heater like a gas boiler you lose some energy in the flue etc. so your efficiency might be 90%. For an electric immersion heater you lose very little energy so the efficiency might be 99.5% - close enough to 100% to make no difference. For a heat pump you also gain the energy you've taken from A so the efficiency might be 200% or 300%.

The closer that the temperatures of A and B are, the easier it is to pump heat from A to B. So the efficiency of a heat pump varies depending on the temperature either side.

Here are some made up examples. Please don't think they represent real systems.

Imagine it's 10 degrees C outside and you want your heat pump to supply warm water for underfloor heating at 35C. The temperature difference is only 25C and your heat pump might be 400% efficient.If the outside temperature fell to -10C, the temperature difference is now 45C and your heat pump might be only 200% efficient.

If instead, you wanted your heat pump to supply water at 55C for radiators, with a temperature outside of 10C you've already got a 45C temperature difference and you'll see 200% efficiency. If the temperature falls to -10C you might get as low as 100% efficiency - no better than an immersion heater.

And this is one reason why people choose underfloor heating with heat pumps, rather than radiators.

Please excuse the inevitable typos, I can spell but my typing is terrible.

Reed_Richards

Air to water heat pump (Air Source Heat Pump)
I have one of these for six months and so far it has worked very well.  I use it with radiators (and a hot water tank).  Underfloor heating would be better for efficiency but you would need that throughout.  It has to be the "greenest" option in your list because you get roughly three units of heat per unit of electricity (on average).  The big disadvantage is that the upfront cost is high.

Air to air heat pumps
This is basically an air conditioning unit (of the right type) run in reverse to provide heat.  It's the "eco-warrior's" choice because it is even more efficient than an air-to-water heat pump but you would struggle to find a company that could plan the positioning and heating capacities required for you, so you would have to do a lot of that yourself.  

Haveyougotenoughtime

Brilliant insightful answers - thank you.

We're not currently on the gas network to answer your question @Gerry1
I'm not particularly bothered about potential buyers, I'm more concerned about the climate emergency we currently face - thanks for your info though :-)

@Reed_Richards and @QrizB - the approx. 10K installation costs - what does this include?

i.e. - how much would it be to install:
- an Air to Water Heat Pump
- underfloor heating (in 5 small rooms - no bigger than 3.5m)
- and a hot water tank

Thanks.

Gerry1

A couple of snippets...

• Apparently Air to Air heatpumps don't qualify for the RHI but do need planning permission.  Presumably this is because they can be used overnight for cooling, and the noise could be problematic for the neighbours during hot summer nights with the bedroom windows left open.
• Wet underfloor heating may not necessarily suit your lifestyle.  You can't set it to switch on half an hour before arriving home in the evenings and expect it to be warm as toast when you open the front door.  You'll probably need to leave it on most of the time because it will be slow to respond.  If you're out all day, big radiators are probably better; not quite so CoP efficient, but probably more than offset by the shorter operating hours. @matelodave dave has several posts on this subject.

Reed_Richards

Sadly, I think the £10k installation cost is too optimistic.  It cost me over £16k to install a heat pump, hot water tank, radiators and new pipework in a 4 bedroom bungalow.  Now the good news (for me) is that I qualify for a subsidy called the Renewable Heat Incentive which will pay a lot of this money back over 7 years.  In my case this will amount to slightly over £1400 per year for 7 years, possibly increasing if electricity prices increase.  The RHI is still available if your house meets the qualifying criteria and you use an MCS-accredited installer.    

Haveyougotenoughtime

...ok - well thanks for all your answers!

Reed_Richards

Grants are available in Scotland and Wales but in England it's only the RHI (AFAIK): 
https://www.edfenergy.com/heating/advice/air-source-heat-pump-grants

shinytop

I can't add much to what others have said but have experience of an ASHP with radiators and with storage heaters.

The ASHP has only been in 4 months so I have no experience of a winter but it has been great so far. It has provided plenty heat and HW over a cold spring and so far running costs are OK.  As others have said the downside is the up front cost.  I would guess £12-15k at the moment for you.    

The storage heaters it replaced were, frankly, rubbish.  They are fine if you want your house hot during the day but cold in the evening. You can get ones that can boost using peak price electricity but they are expensive to buy and run.  Off peak electricity is not the bargain it was either.  I expect the ASHP running costs to be about half of what the storage heaters and the extra evening heating I needed were.  To give you an idea, that's (very roughly) £2k -> £1k

You should improve your insulation as much as you reasonably can whatever system you choose.  

Although I have one, I'm not an ASHP fanboy and would have gas CH if I could.