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Wind/solar powered heating

 
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stumuz1



Joined: 07 Jun 2016
Posts: 668
Location: Anglesey

PostPosted: Fri Oct 26, 2018 12:18 pm    Post subject: Wind/solar powered heating Reply with quote

Has anybody got any ideas for this.

A house has a twin coil tank for hot water. Fuel solar and wood. So the hot water requirements are satisfied.

The house has a condensing boiler for the central heating system.

How could a 80litre tank of preheated water (solar and wind) be incorporated into the central heating system?

A few thoughts to kick things off.

The water in the 80 litre tank could be connected to the cold water inlet to the boiler. However, the central heating system is already filled with cold water so probably would not draw the hot water from the tank.

or

the 80 litre tank could be incorporated into the central heating system effectively becoming another radiator. However, when the preheated water was gone, the boiler would heat up the 80 litre tank maybe cancelling any gains of using the preheated water?

Any other ideas?
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adam2
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Joined: 02 Jul 2007
Posts: 7794
Location: North Somerset

PostPosted: Fri Oct 26, 2018 1:27 pm    Post subject: Reply with quote

There is no simple way to add solar thermal to an existing central heating system.
Such systems re-circulate the same water there is no "new" water to preheat.
Operating temperatures vary a great deal, but about 60 degrees return into the boiler and about 80 degrees heated flow from the boiler into the radiators would be typical.
Much too high for solar thermal to add anything useful during the heating season.

If a significant surplus of solar thermal energy is available, then it MIGHT be worth installing one or two dedicated hot water radiators that are connected only to the solar thermal system. These need to be very generously sized so as to emit useful heat at a much lower temperature than is usual in modern central heating.

In the case of heating domestic hot water, then solar thermal CAN preheat the incoming cold water before it is further heated by a boiler.
This can be done by a very large hot water tank with at least two coils. The bottom coil is heated by the solar thermal collectors, and the middle or upper coil by a stove or boiler.
Solid fuel stoves often have a minimum size of connected hot water storage for safe operation. With a multi-coil hot water tank, only that part of the tank ABOVE the coil counts.
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adam2
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Joined: 02 Jul 2007
Posts: 7794
Location: North Somerset

PostPosted: Fri Oct 26, 2018 1:39 pm    Post subject: Reply with quote

If a SIGNIFICANT surplus of electricity from wind power is available, this can be most useful for space Heating.
About 1Kw needs to be regularly available to justify the trouble and initial expense.

I would not try to add renewably generated electric heat to an existing central heating system.
Simply use one or more electric heaters, that by warming the room will reduce the gas burnt by the boiler.
This is also a slight "doom prep" in that some, probably very limited, heating will be available without reliance on the gas supply.

Smallish wind turbines are seldom competitive with grid electricity at about 15 pence a unit, they are even less likely to be competitive with natural gas at about 5 pence a unit.
OTOH a wind turbine is a useful doom prep, and natural gas is becoming more costly.
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stumuz1



Joined: 07 Jun 2016
Posts: 668
Location: Anglesey

PostPosted: Fri Oct 26, 2018 5:40 pm    Post subject: Reply with quote

You're right!

Thanks Adam
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fuzzy



Joined: 29 Nov 2013
Posts: 1153
Location: The Marches, UK

PostPosted: Fri Oct 26, 2018 7:02 pm    Post subject: Reply with quote

I would run the hot tap for the kitchen sink, the bathroom hot tap, the cold feed for an electric shower etc from a 'solar' tank. If the boiler is an instant heat boiler [commonly called combi and condensing, although it could be neither], then every turn of the kitchen hot tap is firing up/wearing out a boiler and then you have to run a gallon just to pull hot through the house. OK it's just a relay wearing out, but how many gas gurus replace a faulty £3 relay? about zero. A kitchen hot only needs to be warm enough to melt beef-fat for washing up.
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clv101
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Joined: 24 Nov 2005
Posts: 8532

PostPosted: Fri Oct 26, 2018 8:22 pm    Post subject: Reply with quote

adam2 wrote:
I would not try to add renewably generated electric heat to an existing central heating system.

We dump all our excess photovoltaic energy into the hot water tank, minimal infrastructure and keeps us in hot water and can be used for space heating via radiators.

Our 360L tank can hold around 30 kWh (delta from 20 to 85 degrees). That's a larger store than our batteries and a usefully sized dump for our 6.4kWp PV system.
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BritDownUnder



Joined: 21 Sep 2011
Posts: 631
Location: Hunter Valley, NSW, Australia

PostPosted: Sat Oct 27, 2018 8:41 am    Post subject: Reply with quote

For me the best way of using solar or wind electric is keeping it in some form of electricity. I thought that battery charging wind turbines always had a dump resistor in the charge controller. Maybe just use this 'resistor' to generate useful heat, perhaps put in some underfloor heating or a large low temperature tank of water located somewhere in the building possibly disguised as a table or bench. Or you could just use a wall mounted radiant heater. A 2400 watt 240 volt AC could easily handle all forms of low voltage DC from a wind turbine or a solar PV panel.

With the pace of technology there are other more complex means such as inverters or PWM controllers but good olde resistive heat is quite simple to install and maintain..
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