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Author Topic: Proposed Solar Thermal System - unorthodox use of upper coil  (Read 2630 times)
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Posts: 7

« on: March 16, 2016, 09:12:12 AM »

Ok, so the plan is to connect solar primary circuit to lower coil in an Oso Solarcyl unvented cylinder, which will provide the DHW. So far so good, all as normal. The twist is that I have a 300l Megaflo Direct cylinder that i want to use as a thermal store (because I got it for free).

What would happen if I used the upper coil in the Solarcyl to take heat from the solar unvented cylinder and pump it into the Megaflo which would act as a tank containing the space heating primary circuit water? This would only happen when the DHW Solarcyl cylinder has satisfied temperature DHW. The upper coil is in the middle so there should still be a bit of hot DHW in the top?

The upper coil in the solar twin coil cylinder is meant to be used the other way round, to put heat into the cylinder (from a boiler or whatever), so I wonder how effective it will be to 'steal' heat from the heated up DHW unvented solar cylinder using that upper coil? The 'transfer pump' would only operate whilst there is still heat coming in from collectors into the solar primary circuit.
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Posts: 398

Osmington, Dorset

« Reply #1 on: March 16, 2016, 09:42:01 AM »

I do something similar with my two stores; both have a solar coil and they are used appropriately by the Resol controller. 

My DHW only runs through a coil in the larger of the stores (it's indirect) so I have a temp difference controller on the two tanks and transfer the heat from the smaller one by pumping the
fluid contained in the larger through the top coil in the smaller.  At the same time, a destrat pump works on the smaller tank to circulate the internal fluid there.

The same thing also works in reverse; if my WBS gets the large store up to 90, then the same system kicks in to dump the heat from large to small if possible.  At some point, it'll then get transferred back.

2.940 kWP (Sharp ND210/Solis 4G 2.5)
2.115 kWP (Kinve KV235-60P/SB1600)
2.000 kWP (Sharp ND250/SB1600)
65 x 58mm SunnPro/Torrent T280 RE OV/SunSpeed2 205
11kW Dean Forge Croft Clearburn 10,000 BTU
SoFar ME3000SP/Pylon US2000 19.2kW
immerSUN 2
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Posts: 6775

« Reply #2 on: March 16, 2016, 11:10:45 AM »

I  have much the same thing.  The solar panels  connect to the  solar coil in the  DHW cylinder and the heat dump transfers heat to the separate buffer tank.  There is a separate  difference controller that  transfers heat back.  Very occasionally the pump will stay running for a while because both controllers are switching it on.    It is a lot better than a heat dump  because  the heat gets used eventually.    It is probably best for the pump direction to be to take water from the  top of the reserve tank coil  because it is less likely to be warm  at the bottom.  The heat dump sensor in the main cylinder  only senses the   temperature at the bottom of  its coil  and the reserve  tank has the sensor on top and compares the temperature  to the  bottom of the  main cylinder coil.           

DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
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Posts: 7

« Reply #3 on: March 16, 2016, 01:23:26 PM »

Ok, thanks for your responses, So, to make this clear, i will be able to satisfactorily Remove heat from the Solarcyl DHW cylinder using the upper coil by pumping from the cold inlet of a direct cylinder into the upper coil and out into the hot outlet of the direct cylinder?
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