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Does anyone know anything about heat pumps?

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Does anyone know anything about heat pumps?

Huh
11 REPLIES
pierre_pierre
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Re: Does anyone know anything about heat pumps?

Its like a giant Fridge working in reverse. it takes heat energy from a low temperature source and releases it to a higher temperature place - building, house etc
Going back a long time, the Royal Festival Hall on the South Bank - London is heated by a heat pump, it gets its heat source from the River thames
Have seen a house system that has a several hundred metre pipe buried in the garden a couple of metres down
a down side is that it reduces the temperature of the outside ground by a degree or so
pierre_pierre
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Re: Does anyone know anything about heat pumps?


http://www.guardian.co.uk/technology/2006/feb/02/comment.guardianweeklytechnologysection2
Quote
Heat pumps are not so new, even in Britain. The Royal Festival Hall was heated and cooled at the expense of the Thames, using heat pumps, when it opened in 1951, although the system was later replaced with a conventional one.
A friend in Berkhamstead in the late 1950s had the almost unheard-of luxury of central heating, courtesy of a heat pump, with a heat source/sink in the garden, and a walk-in cooled larder as a heat source. It seemed to work well, although he did say that milk froze if two people had baths in rapid succession.
David A Bender University College, London
· Reading your article on heat pumps made me feel I had been transported to a parallel universe where the laws of thermodynamics have been suspended.
The heat in the ground is free, but the energy needed to recover it is high-quality energy, which costs far more than a cheap heat source. You pay 8.4p per Kwh for the electricity to run the heat pump against 1.9p per Kwh for town gas or 2.5p (average over the last year) for heating oil. Even allowing for a 4:1 return on the electricity (3:1 is more realistic) and 90% efficiency of a gas boiler (95% for a modern oil boiler) the margin of heat pump over traditional systems is slim to non-existent and does not begin to cover the loss of interest on the enormous capital outlay. If the sample family expects to replace a £1,000 oil bill with a £250 electricity bill they are in for a shock!
Colin Rourke University of Warwick
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Re: Does anyone know anything about heat pumps?

Quote from: pierre_pierre
a down side is that it reduces the temperature of the outside ground by a degree or so

I’ve seen one induce a permafrost layer, killing off a section of the garden. On the upside it saves on lawn mowing Crazy
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Re: Does anyone know anything about heat pumps?

Modern heat pumps do not have to have coils in the ground, you can get air source heat pumps
http://www.energysavingtrust.org.uk/Generate-your-own-energy/Air-source-heat-pumps
jelv (a.k.a Spoon Whittler)
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Re: Does anyone know anything about heat pumps?

Ground source heatpumps are still used, these come in two varieties, shallow trench or deep bore, the deep bore variety are far better but vastly more expensive to install (these are popular in places such as Texas where oil drilling is commonplace as there are plenty of local drilling companies who will bore to the necessary depth for a relatively modest sum.  If you go deep enough the temperature is very stable all year round.  Water source is still used sometimes (utilising a lake or river though mistakes have been made causing frozen ponds and summer fog).
Air source is often quoted as the most efficient but the performance and efficiency both drop as the outside temperature gets lower (it's more difficult to 'suck heat' from a colder source) so systems often end up supplimented by electric heat to compensate for the lack of performance in the depths of winter, air-source units also freeze up (condensation forms on the cold surface that is absorbing heat from the air, this eventually turns to ice (depending on the temperature outside but normally below around 5 to 7 °C), the layer of ice reduces performance so intermittently needs to be removed, usually be reversing the heatpump system (air to air systems usually also work as airconditioners) using heat from indoors to melt the ice, this also necessitates the use of electric heat to counteract the cooling effect of the defrost cycle.
Air to water heatpumps are no good for radiator systems as they generally do not produce water at a high enough temperature (if they did then efficiency would suffer too much, again some are supplimented by immersion heaters), they do work well with low temperature under-floor heating but again, performance is lowest when most needed in cold weather.
Don't forget, much of UK energy generation is from oil and gas, often at 30 to 40% efficiency with substantial CO2 emmissions so heatpumps working from the electic supply are not as 'renewable' or environmentally friendly as is often implied.
My preferred system: a condensing gas fired warm air heater (around 95% efficient) combined with a heatpump, the heatpump has lower output but is cheaper to run in mild weather, the gas heater is used when the heatpump no longer provides sufficient capacity or looses efficiency due to defrost cycles etc.  All controlled by a relatively simple electronic thermostat that uses an outdoor temperature sensor to switch between the two heat sources at the appropriate outside temperature.  This system also provides cooling in the summer if required (for those that can afford the electricity to cool their home).
Call me 'w23'
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Re: Does anyone know anything about heat pumps?

The combination that makes sense to me is air source heat pump for constant background heat combined with photovoltaic. During the summer when you don't need as much heat you'd be getting paid more for your excess electricity you put back in to the grid.
Gas systems are good - if you are somewhere with mains gas. Not sure I'd be so happy using LPG as you are fully exposed to the price changes of the local supplier.
jelv (a.k.a Spoon Whittler)
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Re: Does anyone know anything about heat pumps?

Quote from: jelv
Not sure I'd be so happy using LPG as you are fully exposed to the price changes of the local supplier.

Good point for those not near mains gas (probably the same poor individuals with 'rural broadband'), woodburners are good if you're right out in the sticks.
Call me 'w23'
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Community Veteran
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Re: Does anyone know anything about heat pumps?

We're looking to move at the moment - probably somewhere around north Dorset, so we are considering all these options. Air source heat pump for the background heat combined with a wood burner looks a good.
(PS Anyone interested in a 4 double bedroom, two bathroom, office, an extra family room and large garden near Burgess Hill, W Sussex?)
jelv (a.k.a Spoon Whittler)
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itsme
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Re: Does anyone know anything about heat pumps?

Quote from: jelv
The combination that makes sense to me is air source heat pump for constant background heat combined with photovoltaic. During the summer when you don't need as much heat you'd be getting paid more for your excess electricity you put back in to the grid.

It's not just the excess you get paid for but all electric produced with a percentage at a higher rate, an additional 3p per kwh, for the what is estimated to go back into the grid. There is no meter measuring the electricity going back into the grid and if you have an old meter it will start to run backwards.
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Re: Does anyone know anything about heat pumps?

Quote from: walker23
If you go deep enough the temperature is very stable all year round. 

You don't need to go to deep, we’ve a 10000 ltr reservoir under our greenhouses, the water temperature  throughout the winter seems to stay at around 6deg C, although the outdoor temperature has dropped to -15C the reservoir does prevent the greenhouses dropping below zero.
I don’t actually find wood burners that efficient/economical, a large wheelbarrow load of wood (Mountain Ash or Oak) last an afternoon/evening compared with a small bucket of coal 'nuts' the wood does not give off as much heat.
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Re: Does anyone know anything about heat pumps?

Some air source heat pumps I've seen can be reversed in the summer to keep the house cool.  They're reckoned to be a good relatively low energy method.  The sorts of efficiencies I've seen bandied about talk about 1Kw of electricity to give the equivalent of a 4 Kw heater.
John