We're thinking of having our kitchen and utility rooms refitted, and as part of that, my wife wants a new boiler. We have a 34 y/o Trianco Stuart oil boiler, which the maintenance man each year sucks his teeth and witters about having a new one, and each year we ignore him.
We also have a well. About 35ft deep and 4ft in diameter and almost completely full of water. I've always thought it would be a nice idea to put a heat pump down it and save some oil.
Although I understand the principles, I know nothing about the specifics.
On average heat pumps consume one third of the electricity of electric resistance heaters.
Economy is improved by operating heat pumps using overnight off-peak electricity, storing heat in a large thermal-store of water to be used during the day.
Efficiency
This is slightly confusing, as there are three efficiency acronyms to note: COP, SEER and HSPF. The COP is the important figure. The COP - Coefficient of Performance, based on kW of electricity consumed and kW of heat produced.
Performance - COP
The COP relates to electrically driven heat pumps. The efficiency performance rating is the Coefficient of Performance, the COP. As a guide, electricity is 100% efficient in that all the energy used at point of use is converted to power or heat. An electric immersion element heating a hot water cylinder has a COP of 1. A natural gas boiler will be approximately COP 0.85. The higher the COP the more efficient the heat pump. A COP 4 rating means that for every kilowatt of energy consumed four kilowatts of heat is extracted. Some manufacturers are claiming COP 7.
Generally, heat pumps with the highest SEER and HSPF ratings are more expensive to purchase. However, because of low electricity consumption, economics in the long-term are more attractive.
Ground Source Heat Pump
Geothermal heating and cooling. Heat is extracted from the ground, which has predictable stable temperatures. Conversely, heat may be dumped into the ground when cooling a building. Heat is extracted by installing a plastic pipe loop horizontally or vertically in the ground. Ground-source heat pumps work well no matter what the air temperature, because the ground temperature does not drop much below 10C in the United Kingdom at a depth of 1.3 metres. Incorrectly designed or sized pipe loops can over-cool the ground surrounding the pipe, leading to much lower outputs and efficiencies.
It is possible to freeze the ground around a ground loop lowering efficiency. It is preferably to have inactive periods to allow the ground temperature to recover preventing ground freezing. When the temperature of the ground is lowered sufficiently, the COP rating will drop.
Using three to four times less electricity to run than conventional electrical systems, on the surface appears highly attractive. However, appearances can be deceptive. Running costs are likely to be higher than a condensing gas boiler system when used for heating purposes. The best case example of a water sourced heat pump may equal or slightly improve on natural gas running costs. Despite a gas boiler having a COP of 0.85 and a heap pump say COP 3, natural gas per kWh is approximately 4 times cheaper than electricity. Running cost comparisons to oil depends on oil prices, which may fluctuate greatly depending on the season and world demand. Overall, heat pumps cost more to run than an oil boiler.
Although a heat pump may equal the running costs of a natural gas boiler, in the UK the big problem is the extremely high installation costs, which may be three to four times the cost of a typical gas fired system. Heat pumps as yet, cannot compete with the installation costs of boiler and forced-air heat recovery and ventilation systems fuelled by the three main fuels of natural gas, oil and liquid petroleum gas (LPG).
Water sourced heat pumps are efficient as more heat is in water. But, a well with no running water may freeze over. It may be worth your while having a pump to pump well water out and say into a stream if the well automatically fills up of course. Then no freezing of the well and constant supply of heat.
Our system is a straightforward ground-based system - loadsa pipe buried 4ft below the surface of the ground - we needed to do an amount of earthmoving anyway as part of a bigger project - so the earthmoving costs were spread over the various works.
From a breif look around the web it seems that well-based systems (at least in the references I could see) work by drawing water from the well, extracting the heat from it, and then returning the water either into another well, or into a river, soakaway etc. There are systems which use a series of shafts to house the collectors - but they seem to be narrow, deep shafts, rather than 'old wells' like yours.
It's a tiny part of the expense, but you'll probably find that you need a new hot-water tank as part of the heatpump installation. Heatpumps get unhappy if they can't dump their heat quickly - which means that they like a large surface area in the heat exchanger coil in the hot water tank - round about 2 sq metres in our case. The 'conventional' tank we have at the moment (ex oil-based system) had about 0.5 sq metres surface area....
Maybe take a look at the links above and follow up some of the suppliers ? I didn't see grants specifically for well-based systems - probably worth discussing that with a potential supplier...
If you can't do well-based then you need a fair ground area to bury the pipework in - depending on how much heat you need to collect.
Well based systems can be either 'closed loop' or 'open loop'. In the closed systems a working fluid is circulated down the well in a sealed pipe. These closed loop systems are commonly used in household installations. Larger installations are often open, with water being pumped out of the ground and then returned via a second borehole. Typically the quantities of water involved in large systems mean abstraction licences are required.
If you have an existing well you should be able to calculate whether, given the depth of well, the water level and local geology there is sufficient thermal capacity to run a given heat pump. I would guess that at 35 foot you may be at the shallow end - most GSHP bores seem to end up 25 metres or more in depth.
I don't know but one of the two local schools went this way in the summer holidays. The other got one of those wood pellet boilers.
The heap pump one got a 70m shaft one and the comments about the lovely warm school in the morning are impressive.
The pellet burner blew up on Monday with a very deep loud WHOOMP noise and large cloud of smoke. It destroyed itself and they have had no heating/water since.
Although it seems like, once again, we're looking at a 20 year payback, in which case a more efficient oil boiler and lots more insulation would make more sense.
Why is that a problem unless, like a B&Q wind turbine, you don't expect the installation to outlive it's payback term? Even if you sell up before then, it's surely a selling point, not needing regular oil deliveries.
Do you use the well for hosuehold water? Even if you only ran the loo cicterns of it you could save a fair bit on your water bills. I once calculated that more than half our wtare consumption went into th eloo cicterns, although that was in the days of big flush cisterns.
One of the attractions of a heat pump ought to be the near-nil maintenance and repairs, saving both money and hassle. Also when comparing with oil, not having to arrange oil deliveries and providing space for a tank (which may or may not be problematic depending on location).
Having looked at the economics, I decided it wasn't worth using any form of heat pump, except possibly air conditioning used in heatpump mode. However SWMBO doesn't like aircon at all, so that's out.
What did work out as cost effective was a f*ck-off big thermal store, with solar panels, and a thermal-siphon setup with a log burner. This costs a fraction of the price of a heatpump setup and can provide useful boost to the heating system all round the year.
I'm also tempted to try to create my own solar fence having experimented with around 100 metres of black tubing laid on the ground. That is, I would set up concrete posts oriented East/West and string tube between the posts. Then I can pump water through the tube on sunny days. Not as efficient as a panel but good enough for preheating water.
Indeed, if you are prepared to pump the groundwater the depth of the well, per se, is irrelevant. You would, however, be adding the cost of pumping the water, assuming the well had adequate yield , and you would also have to dispose of your 'waste' water, which is normally done through return via another well or discharge through normal drains. At some point, probably round about the requirements for a 5 bedroom house, the amount of water required for an open loop system would make an abstraction licence necessary. Any pumping, licensing and 'waste' water disposal will affect the overall economics.
I'm not sure how these licences work. If you pump out of one well into another, there is no water abstraction. The most efficient heat pumping method is extracting heat from moving water - if you have a moving stream of only 6 inches deep then pipes on the bottom will be effective. So, any pumping losses would most likely be more than offset by the extra heat gained.
You could have a largish insulated tank; above or below ground. Pump water from the well into this tank, so it is the same temperature as the well water. A differential controller will operate the pump. The heat pump extracts heat from the tank and keeps the COP at the highest. The COP falls off when the ground/air/water cools around the slinkies/collectors. Different temperatures of water is easy to move and extract heat from. This tank could also be coupled to solar panels too, which dumps heat at the top of the tank.
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