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Given the prices you quote, I thought you were already talking heat pump electric... For plain electric, it's a rip-off. For heat pump, it's the price of the hardware (you'll pay just as much to have the collectors buried under your lawn ... No lawn ? you're, er... probably fucked, sorry, deprived of the most efficient heating system, like most urban dwellers)

Pierre
by Pierre on Mon Jul 10th, 2006 at 06:39:35 AM EST
[ Parent ]
It's all flats where I live, mate.

I looked up "heat pump" on wikipedia, and found this:


Note that when there is a wide temperature differential, i.e. when heating a house on a very cold winter day, it takes more work to move heat indoors, and it is possible that a heat pump's COP would be below 1 in such a case. In other words, when it's extremely cold outside, it's better to just make new heat indoors using a conventional heater, than to try to take it from outdoors using an air-sourced heat pump.

My ignorance on such topics is, well, now stated, but living where it can get cold for more than a couple of months every year, and where we heat a flat with radiators, which have their water heated by gas, which has gone up in price by 25% in a year, I like the concept of underfloor electric heating.

A search on google for "electric underfloor heating" brought up a load of businesses (so my non-investment investment has already been made by others.)  I clicked on a link, found a Q & A, and read this, relating to bathroom underfloor heating:


Question

Isn't it expensive to run ?

Answers

The devimat® tile warming system only uses as much electricity as a standard light bulb per m². The on-off cycling effect of the floor temperature-sensing thermostat can reduce this by as much as 50%.

It seems a huge market (and as gas prices rise, an ever-cheaper heating resource) for people who live in flats, though maybe not an idea for people who live in detached properties.

I don't see the "rip off" aspect.

Don't fight forces, use them R. Buckminster Fuller.

by rg (leopold dot lepster at google mail dot com) on Mon Jul 10th, 2006 at 07:55:36 AM EST
[ Parent ]
(Note I over-stated the prices by a factor of TEN (ouch!)in the orginal post, due to, er, human error on my part.  The correct figures (I added them in an addendum post) are:

Electric underfloor heating mat = approx. £1,400, or approx 2000 euros.

(I quickly check the zeros...yes, they are correct.)

The flat (not mine, one I saw) is between, say 60 - 90 square metres (lots of rooms in funny places, and I'm no good at guessing room sizes), and had no heating system installed (apart from two hundred year old fire places.)

Don't fight forces, use them R. Buckminster Fuller.

by rg (leopold dot lepster at google mail dot com) on Mon Jul 10th, 2006 at 07:59:56 AM EST
[ Parent ]
Actually, you have the problem of COP<1 only with the "cheap" (that is 5000 €) heat pumps fitted on the balcony, and which try to exchange heat with the atmosphere like an air conditionner. They practically stop working at 0°C because of frost on the exchangers.
"Real" heat pumps take the heat from 1.5 m underground, where it's 10°C almost all year long, with burried pipes (that's where you need a lawn and big work $$$). You may need additional fuel heating a few days/weeks per winter if you are in a really cold area where the ground freezes in the winter (like: there is 20" of snow on you lawn for 2 months every winter...)
There is still a variant to fix this problem: the heat well heat pump, with a few 50-100m wells which get the heat from the waterbed, which never freezes in any  place that actually has grid power (Siberia is a special case...). And you actually need less lawn area to conceal those wells, but they're even more expensive to drill (expect 20-30k€ for a mid sized house - you may have a tax rebate on this in some countries).

Pierre
by Pierre on Mon Jul 10th, 2006 at 11:53:24 AM EST
[ Parent ]
That sounds awfully expensive for just the well...

I have just contracted a company for drilling a 650 feet deep well for a 9kW heat pump. The drilling cost is about €5500 or $7200. The heat pump costs about €7500 ($9600). Add installation and the total is about €15000. I already have radiant floor heating and radiators since I've been burning oil until now.

They don't usually drill multiple wells here unless you need more than ~700 feet depth which means 11kW pump and up.

Year average COP should be about 3.5, time to earn back is about 10 years with todays oil price, much less if it hits $100 :)

by jkirkebo (jkk@scm.no) on Mon Jul 10th, 2006 at 06:34:01 PM EST
[ Parent ]
I was thinking of the price for the complete setup (couple of 50-m wells, heat pump, low temperature radiators, possibly solar-hybrid with hot water). Well-collector heat pumps have much higher COPs these days: Viessmann claims up to 6-7 (but that brand is really pricey).

Pierre
by Pierre on Tue Jul 11th, 2006 at 03:27:57 AM EST
[ Parent ]
Peak COP and year average COP is quite different. You'll never get the higher COP when producing hot tap water in the summer. Also a some brands don't include the power consumed by the circulation pumps when calculating COP :(

I've never heard someone reporting a year average COP of more than 4. Still, when already at 3.5 or so, higher COPs mater less and less. The difference in savings from 2 to 3 is huge, from 4 to 5 is miniscule in comparisation.

by jkirkebo (jkk@scm.no) on Tue Jul 11th, 2006 at 04:05:49 AM EST
[ Parent ]
It's true COP doesn't matter on the power savings side, but it helps in that you can heat a bigger space with a pump of a given size (you save upfront cash on the collector, you save room in you basement, you need less of complementary heating, things like that... and also, I like the best technology, better have it in heat pumps than in sport cars !)

Pierre
by Pierre on Tue Jul 11th, 2006 at 04:21:24 AM EST
[ Parent ]
BTW, why do two 50m wells ? A single 100m is far cheaper and just as efficient. Only when one requires more well depth than the max collector length (usually 400m/1312 feet) can support it makes sense IMHO.
by jkirkebo (jkk@scm.no) on Tue Jul 11th, 2006 at 04:09:01 AM EST
[ Parent ]
Viessmann has a system of variable flow rate pumps, so they save on the flow pumps by switching off a well if it's not needed. And you have less load loss with shorter parallel fluid circuits than with a single long one. For horizontal collectors, they also have between 1-8 separate circuits, depending on the heat pump size, for the same reason.

Pierre
by Pierre on Tue Jul 11th, 2006 at 04:17:06 AM EST
[ Parent ]

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