/ Air source heat pump

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Philip on 18 Apr 2014
Hopefully moving house to somewhere we will stay for a very long time. I've been through this exercise with my current house where we never intended to stay more than 5-10 years.

I want to install central heating to a property without mains gas. It needs to be a system that works without someone there (not a coal/log fire and back boiler). Cost not a concern, if payback is good (considering renewables).

I'll be removing storage heaters, and disconnecting coal fire back boiler. (Although eventually this will become a log burner and I would later like to couple this in to help provide hot water).

Space inside is not easy, although it's a large house, there is a hot water cylinder, but I don't want an internal boiler if I can avoid it. Space outside is almost limitless. Roof is E and W facing.

I originally though oil, external boiler. Probably combi or unvented tank. Great mains water pressure. But I'd be interested from anyone who's fitted a heat pump either on its own or with some other heat source. I don't want downstairs underfloor heating as it means ripping up expensive flooring - but I see Dimplex do radiators that work at 40 degrees C.

My only worry with heat pump is that I'll be using a lot of electricity if I have heat pump + 1 or 2 electric showers + electric cooking. In my current house the electric boiler and shower are connected by relay to prevent simultaneous use.

Anyone on here tried biomass?
Ferret on 18 Apr 2014
In reply to Philip:

I know nothing about this stuff realy but I do have a friend who has recently as part of his rennovation put in a biomass system (I think he simply uses logs from his land but there are various options revolving around logs or pellets). In an external boiler house I think there is some form of automated plant that burns the biomass as required, its all hopper driven/self feeding etc. That then heats water in a huge (several thousand litres I think) and super insulated tank.

I don't know how long you can leave it truly unatended (i.e. I have no idea if it is self lighting/self clearing etc but I suspect it needs a little care and attention) but certainly through summer the theory is that you only boil up the storage tank once every few days as when demand is low it lasts ages. In winter you probably heat it more regularly but again only a little to bring back up to temp as heat is used. I think the tank does underfloor heating so that would also work with low temp radiators and provides hot water.

Ideal where space really is unlimited as you can have a boiler house and plenty storage for whatever mass is being used. In his case it was a full on rennovation so I suspect the house is also very insulated which is hard to do as a retrofix type option and cost benefit stuff may depend on if you have biomass youself or have to buy it in. Wood chips/logs by the lorry load into a big storage hopper with a wormscrew feed system or similar is cheaper and easier than buying in bulk bags however.
JJL - on 18 Apr 2014
In reply to Philip:

From what you describe I'd suggest:

Large thermal store (in loft or cellar if you have one); with tappings to connect stove boiler later.

Thermal hot water tubes on W roof.
Photovoltaics on E roof, and one of the gizmos that monitors output and directs excess into an immersion input in the store.

If you have space, I'd probably go for ground-source heat pump.

All this comes after proper insulation of course.

J
cb294 - on 18 Apr 2014
In reply to Philip:

Ground source heat pumps are typically much more efficient than air source ones, better degree of coupling. What would put me off an air source is the noise. Muffling has generally become better, but the compressor from the neighbours´ heat pump when I am at my parents place drives me insane.

CB
JonnoP - on 18 Apr 2014
In reply to Philip:

Have sent you a message with some more detail but thought it worth pointing out the differential in efficiency between air source and ground source systems.

Given a UK property that has been appropriately improved insulation wise and a properly designed system, the difference in seasonal performance between the two is marginal.

This is because the average winter temperature in the UK is about the same as the design temperature of a closed loop ground source system.

It's worth looking at the Energy Saving Trust phase 2 heat pump trial report.
Philip on 18 Apr 2014
In reply to JonnoP:

Thanks for the info. I have a feeling my wife's requirements for hot water are not compatible with renewables!
John_Hat - on 18 Apr 2014
In reply to JJL:
Agreed about the thermal store. You could hook it up to solar, air or ground source heat pump, electricity (as in immersion), an oil fired boiler, and a wood burner, all at the same time and it'll use whatever is the cheapest source of heat at any second.

Add in you'll get mains pressure hot water as well, and - if money is no object - then you'll be not paying a penny to anyone for life.

In terms of cost, we specced out a mahoosive thermal store + solar + a small boiler + a wood burner, all interconnected, centrally controlled, and it was about £25k (including all appliances, control mechanisms and fitting). This was a bit expensive for us at the time and we ran away. Your mileage may, naturally, vary.
Post edited at 17:15
Philip on 18 Apr 2014
In reply to John_Hat:

With the new RHI I think if we do it right the payback is actually short (10years not 20).

A large thermal store seems a good start. The existing coal fire can be left on it until the log burner. Solar can come later. It just a choice of biomass or air/ground source.

I'll need some pro advice as the house will eventually have three bathrooms each with shower or bath, and the kitchen too. My wife likes 30 minute showers or a bath with hot water left at the end for a quick shower. How do thermal stores cope with large demands like baths or long showers?
JJL - on 18 Apr 2014
In reply to Philip:


We've a 5-bed, 4-bath house and two teenagers.
We have a 400l thermal store with PV panels, Solar tubes, log burner with back boiler and a gas boiler for top up in winter.

400l at 70 or 80oC is a *lot* of stored heat.

We use gas in the winter - an 8kW back boiler can't manage the whole house (think rambling Edwardian). We use gas only for cooking approx. April/May - Sept/October inclusive
Philip on 18 Apr 2014
In reply to JJL:

Sounds good. I would need a substitute for the gas. If oil, then I may as well just install oil and maybe the store, then upgrade with time.

Do you get RHI payment on yours?
Daysleeper - on 18 Apr 2014
In reply to Philip:

Avoid ASHPs unless you're made of electric money.

If you have a decent truck access you could go for Pellet fired Biomass, large store with automatic transfer would allow for months of use without any intervention. You can even put the boiler and store in an outhouse and use heat main to bring the hot water in.

However, I'd check the cost of getting mains gas connected, might be cheaper than you think and depending where you are there are grants and discounts available.
Philip on 18 Apr 2014
I'm starting to get an idea now. A heat pump to run full time and heat the heat store. Coal fire on the heat store, to eventually be replaced with log burner. Solar to be fitted eventually to save in summer, PV to offset heat pump energy.

Underfloor upstairs, and maybe oversized or low-temp rads downstairs. With only an air source heat pump, will the thermal store get hot enough for good hot water?

Philip on 18 Apr 2014
In reply to Daysleeper:

Is that up to date info. From what I've read ASHP are much better than a few years ago.

Mains gas is going to cost a fortune to install if they have to run the pipe 5 miles to get to the village. Also, not really a long term solution.
JJL - on 18 Apr 2014
In reply to Philip:

Yes on the pV cells; not on the back boiler as we fitted it too early.

Make about a 7% return on the PV investment with an east facing roof and 4kWP. It'd be more if it faced S.

JonnoP - on 18 Apr 2014
In reply to Philip:

Domestic Hot Water does need as much thought as the heating side. There are plenty of air source heat pump installations out there providing sufficient DHW, whilst maintaining efficiency and heating performance.

With the RHI, combining solar thermal with air source is a very good idea. There are cylinders available with twin coils to benefit from solar and these can be 300l upwards.

An ASHP can produce water temperatures of 55 to 60 degrees for DHW, which is more than sufficient. (They would also have an immersion heater for pasteurisation). The key to good design is to minimise the amount of time it is doing DHW so that it runs at lower temperatures for heating, which is where it is most efficient.
Philip on 19 Apr 2014
I've not ruled out GSHP or biomass. Although the figures are high I'm working on the following. £7k oil would have cost, £500 year fuel saving for not oil, £1000 for at least 5 years from RHI. That makes £14-15k installation quite attractive.

It'll be cheaper if I can pay for a design and use local plumber to install rather than specialist company. The old airing cupboard would do for a large tank. Most GSHP seem to need a second unit, which I guess ASHP have in the outside unit.

A system that also connects a log burner would be best and winter is when we use the most baths, and it's a great way of making hot water. Not sure if this will affect RHI payments. It would be good as I'd allowed further plumbing costs for this that would be lower if done all at once.
JonnoP - on 19 Apr 2014
In reply to Philip:

If you go with a multi-fuel option, all you need to do is meter the heat pump. Stand alone systems only go off the energy usage as detailed on the Energy Performance Certificate.
JJL - on 19 Apr 2014
In reply to Philip:

I think you have to have a registered installer to get the RHI.

Also be aware that if the goods are supplied and fitted, they'll attract VAT at 5%; if just fitted, it's 20% on the goods and 20% on the fitting.
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Philip on 19 Apr 2014
In reply to JJL:

Good point about the VAT. I think I'll try and find one who'll do it all. It'll be easier if they're independent and can source the best of each kind than just tied to someone like Worcester. I'll have to be careful about incurring knock on costs too early. For example the DHW can't be taken advantage of until the bathrooms are converted from electric showers. Underfloor heating upstairs requires new floors, the log burner requires some building work and new floor to sitting room. All necessary, but with oil I could leave a lot of these.

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