Heat Pumps

[johnf]

I have a 25 year old oil fired boiler that is nearing the end of it's life.
So i am starting to think about a replacement or alterative heat source

So the question is does anyone use or have any info about heat pumps there running costs ,installation costs, any snags that I should know about.

I have a 3/4 acre lake close to the property that I understand I can use as a source of heat.

Thanks a lot for any info in advance

 

[RogerS]

John

Rather than re-invent the wheel, if you enter this into Google

"heat pump" site:ukworkshop.co.uk

then you'll get quite a few of the threads that are already on ukw about this. CAT (centre for advanced technology) have books reasonably priced on this.

Roger

 

[MikeG.]

John,

can I suggest that you also consider a wood pellet boiler as a replacement? They are commonplace on the continent, and are gathering interest over here. The pellets are around the same price as oil is (calorie for calorie), and everything is just as automatic as with an oil boiler. Consider also that a wood pellet boiler, although bigger than an oil boiler, is pretty much a bolt-in replacement for your old boiler, whereas the heat-pump would require a vast amount of digging.

Heat pumps are a bit of a fad, and are really a glorified form of electric heating. When the inefficiencies of generation and transmission of electricity are taken into consideration the net efficiency is actually very poor. This may not interest you, understandably.

Mike

 

[SimonB]

We're considering a new build and want to make it as renewables based as possible. At a recent Home/Design type show we spoke to a company (who partner with Robbens) about heat pumps and they advised that for us air source heat pumps would be the best choice combined with underfloor heating which we were going to have anyway. They said that they are more economical than oil, which like you we have, but less than gas. Apparently they can recover heat to -15 degrees C, but how the recovery scales off at that temperature I don't know, is it enough to maintain whole house heating.

The units they recommended were combi heating and air-con and they also have an electric backup to supplement if necessary. I would guess that is probably quite uneconomical.

We were originally interested in ground source heat pumps, but we are planning on landscaping the garden in stages which would complicate having to try to combine the two pieces of work.

At this stage that's all the information we have, and haven't researched alternatives or real life costs/efficiencies and I certainly wouldn't want to contradict Mike who obviously has real world experience with these technologies, but thought I'd pass on the little I've been told.

My partner's brother is an architect and he has pointed us towards a (new?) type of solar based technology (tube things) which he says are very good, but we haven't looked into those a great deal yet either. We're still at the design stage and several related issues have delayed the whole project.

 

[MikeG.]

Simon,

The solar tube sollectors are terribly efficient, but are only for supplying hot water (not for space heating). Thermomax is the market leader. There is a cost/ benefit analysis to be done, though, because they are quite pricey, and some of the slightly less efficient flat panels are a great deal cheaper but are still very good.

If you are trying to keep your new project as renewables-based as possible, then I would also point you towards wood-pellet boilers. Heat pumps are electrical, and are therefore carbon dioxide emitting users of fossil fuel.

Mike

 

[RogerS]

Aren't airsource pumps very noisy? Similar to sitting by the noise from those airconditioning units? IE - I wouldn't want to have that noise constantly in the background and I guess others don't as on one of the air source heat pump sites they make a big thing that part of their unit can be sited 30m away!

EDIT: re noise. Seem to remember reading somewhere about the Govt shifting the goalposts as to what was (clinically IIRC) the maximum recommended background noise, as far as sanity was concerned, from wind turbines. They fudged the figures to be 'acceptable' - although much more than the recommendations - otherwise many land based wind turbines could not go ahead. Are these now going to be the next WMD?

 

[lurker]

Anyone re-thinking their heating methods need to consider some stand alone sytems if only for a back up. Plus consideration of all eggs in one basket.

The UK came very close indeed to electricity outages last Feb & Gas was/is critical at the moment.

Last evening our central heating packed up (gas valve on the boiler evidently) and will not be fixed until tomorrow at the very earliest. Fortunately we have our low tech open fire in the lounge to keep us going.

 

[RogerS]

Anyone re-thinking their heating methods need to consider some stand alone sytems if only for a back up. Plus consideration of all eggs in one basket.

The UK came very close indeed to electricity outages last Feb & Gas was/is critical at the moment.

Last evening our central heating packed up (gas valve on the boiler evidently) and will not be fixed until tomorrow at the very earliest. Fortunately we have our low tech open fire in the lounge to keep us going.

Good point. We use our open fire on a daily basis and that also keeps the ch down low as background heat for the rest of the house. Even if the electricity fails, I have a 6kW generator that will let us carry on as normal (apart from not using the dishwasher).

edit: Given that those heat pumps need quite a high electricity input to drive them (more so than the pump in, say, an oil or wood fired boiler) then you're stuffed in a power cut. That's why I quite like those wood-fired boilers that Mike suggested.

 

[big soft moose]

If you are trying to keep your new project as renewables-based as possible, then I would also point you towards wood-pellet boilers. Heat pumps are electrical, and are therefore carbon dioxide emitting users of fossil fuel.

Mike

only if you run them on national grid electrickery - i remember reading somewhere about a guy who powered his heat pump from a 3kw PV array on the roof - that would qualify as renewables based.

 

[RogerS]

Idly Googling while 'on-hold' I came across this site which seemed quite interesting.

http://www.enviro-friendly.com/

I also liked the smartflo guttering

 

[MikeG.]

We use our open fire on a daily basis

Yeahbut........open fires are a net cooler of the house.

To have a permanently open hole in the house to allow smoke out means that most open fireplaces let between 6 and 20 times as much heat out of the house as they ever put into the house when they are burning. This is much improved if a woodburner with proper flue and a register plate is installed, but even then there is a column of cold air sitting inside your house.

Most houses would be much warmer if the chimneys were removed, and none of the houses I design ever have a functioning chimney for this reason.

Mike

 

[MikeG.]

Heat pumps are electrical, and are therefore carbon dioxide emitting users of fossil fuel.

Mike

only if you run them on national grid electrickery - i remember reading somewhere about a guy who powered his heat pump from a 3kw PV array on the roof - that would qualify as renewables based.

Well, not quite the whole story! Photovotaics in this country take about 12 years to generate the same amount of electricity as went into their production in the first place, so the PV array running the heat pump would for 12 years be essentially running on fossil fuel. Of course, the fundamental flaw with this proposal is that in the winter when you want the heat, the sun isn't shining very much. I suspect that the chap you refer to lives somewhere like Canada or parts of Europe, where winter sun is much more common than here.

Mike

 

[RogerS]

We use our open fire on a daily basis

Yeahbut........open fires are a net cooler of the house.

Yup....and much more fun to look at than a wood-burner.

[/quote]

 

[lurker]

I understand your arguement Mike but our house was toasty yesterday evening. Bluddy cold this morning

Although I buy some coal as backup (about 6 bags per year) the rest of the time the fire runs on scrap wood. Fire runs from Sept to April & at weekends I light it about 11am.
A further point, condensation is unknown in our house & I think that's entirely due to the chimney.

I must admit if circumstances change I'd quite fancy one of those pellet burners.

 

[lurker]

Well, not quite the whole story! Photovotaics in this country take about 12 years to generate the same amount of electricity as went into their production in the first place, so the PV array running the heat pump would for 12 years be essentially running on fossil fuel.
Mike

This is the point the tree huggers overlook and should be accurately calculated for any "renewable"

Land based wind turbines are the work of the devil and when I rule the world anyone who says differently will be providing fuel for anaerobic digesters so damn fast :twisted:

 

[MikeG.]

our house was toasty yesterday evening. Bluddy cold this morning

You make my point for me! You house is cold this morning, in part because you have a hole through the roof.

I shan't make a big deal of this, simply because the vast majority of house in the country have a chimney. I would wish most of them away........but.......that's it......it is just my wishful thinking.

Mike

 

[wobblycogs]

The chimney being a column of cold air is interesting point. Would a solution be to have the chimney external to the building e.g. stood off from the wall by a few cm. I've seen it done with gas boiler flues so presumably it could be done with a stove too.

I'm actually surprised the column of cold air makes that much difference. Our chimney is lined and the liner is surrounded by vermiculite. Feeling the wall I can't detect a difference in temperature where the chimney is when the fire is out. Making stoves draw air direct from outside (like gas boilers) would be a good idea though, we have an air inlet through the wall right behind the stove which means the stove gets air the air it needs but it doesn't freeze the room when the stove is out.

 

[bugbear]

We use our open fire on a daily basis

Yeahbut........open fires are a net cooler of the house.

Really? That seems dramatically counter intuitive.

Surely medieval man would have (eventually!) noticed that all the work he was putting in to getting fire wood was making his great hall colder?

My lounge certainly gets warmer when I light the (open) fire - or at least I think (feel, in both senses) it does.

edit; sorry didn't realise you meant "over all time", including when not lit.

BugBear

 

[wobblycogs]

I read about open fires being a net coolers when we were looking for our stove and I have to admit that I was sceptical at first but the arguments are compelling.

The first thing you have to do is realize you are looking at your house as a whole not just the room the fire is in. An open fire will require a lot of air to burn and that air has to come from somewhere. If you don't have an air brick in the room the fire is in (or some other ventilation) chances are that most of the air is coming from the rest of the house. That causes a pressure drop in the house which in turn sucks cold air from outside. You don't notice this sucking in of cold air though because it's small amounts all over the house and the radiators warm it up quickly. To exaserbate this problem as the hot flue gases from the fire go up the chimney they will suck large volumes of air up with them, that's air that you have warmed with the fire mostly hence the terrible efficiency of an open fire even if the combustion air comes from outside.

Finally, if you look at the really big picture where you talk about not only the whole house but all the time the house is heated when your fire is out the chimney is still drawing (a least a little - ours is like a vacuum cleaner!) so it's sucking heat from your house. So therefore over all you would probably use less energy if you didn't have the fire.

A stove gets around a few of these problems most notably the one where the fire causes extra air to go up the chimney but it's still not perfect. The more convoluted air path means it doesn't draw much when the fire is out and it's generally easier to put an air brick close to the air inlet.

 

[RogerS]

That's why in the Netherlands IIRC they have chimney flues that are concentric. Air for the fire is drawn down the outer ring and also has the benefit of being heated on the way down which improves combustion.