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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorCaterham07
    • CommentTimeSep 22nd 2017
    I have a new four bed holiday house with UFH on both floors managed through two IVAR blender manifolds controlled by two Heatmiser UH3 Wiring Centres. On the supply side I have a Akvaterm Solar 2000 Thermal Store which is only heated by an oil boiler with electric immersion coils as back up at the moment. It has been set up so I have options next year for solar / heat pumps etc. There is a Main Circulation Pump to both move water from the Thermal Store to the boiler but also to take water to the manifolds. It's one loop.

    An ESi Electronic Dual Cylinder Thermostat is attached to the Store but has been added after the original installation and not commissioned properly.

    The Store Thermostat is wired as follows. Perm L&N. The Switch Live "Boiler Out" from the Wiring Centre is going into the HW-On Com terminal in the thermostat. A single wire goes from HWS N/O in the thermostat to a fuse input terminal through to activate theCirculation Pump. The Boiler Switch Live is inserted in the same input terminal and is made Live as the power passes through to the Main Circulation Pump. It works for maintaining the heat store temp for DHW.

    However on the heating demand side, when the Wiring Centres activate, the blender pumps start as required but the Main Circulation Pump does not activate. No hot water is round the loop to the manifold from the Store. Moving the Wiring Centre Switch Live to the Main Circulation Pump Fuse input makes this work.

    What is missing is the ability to activate the Main Pump from either the Store Thermostat and / or the Wiring Centre.

    My thinking has been as follows ....

    Bridge the Perm Live and HW-On COM terminals within the Store Thermostat. Take Boiler Switch Live direct from Store Thermostat HWS NO. Also take a Switch Live from same HWS NO terminal to Fuse input terminal leading to the Main Circulation Pump. Wiring Centre Switch Live to same Fuse Input for Main Circulation Pump.

    I think I will have a backfeed problem because SL for Wiring Centre and Store Thermostat are connected at the Pump Fuse input ?

    How can I activate the Circulation Pump from either or both of the Switch Lives without backfeed ?

    I want to avoid the boiler turned on every time the Wiring Centre calls. I want the boiler to be controlled solely by the Store Thermostat. My concern is SL from Wiring Centre backfeed to Store Thermostat and activates Boiler Switch Live at HWS NO Terminal which they would share.

    I have run out of road on thinking this through and would welcome some advice. Are relays the answer ?

    Thank you for taking the time to read my ramblings ...
    • CommentAuthormattstan51
    • CommentTimeSep 23rd 2017
    I think you are better adding an extra pump that works from the roomstat to circulate to the underfloor heating

    without that you'll be activating the boiler everytime the water goes to the underfloor heating.
    • CommentAuthorCWatters
    • CommentTimeSep 24th 2017

    The two halves of our system work totally independently. They only share the FSU (switch and fuse).

    Primary - The stat on the store controls the boiler and the pump that circulates water from the boiler to the store.

    Secondary - The room stats go into 2 wiring centres. The two "BE" signals are logically OR'd together to control the pump that circulates water between store and manifolds.

    There are no connection between the two sides. If the rooms call for heat the store delivers it without firing the boiler. Eventually the store gets cold and the boiler fires with one long burn to reheat it.
    • CommentAuthorCWatters
    • CommentTimeSep 24th 2017
    I think your proposal can be made to work (isolation can typically be done with a relay) but if I understand correctly you will have hot water from the store circulating through a boiler that's switched off?
    • CommentAuthorCaterham07
    • CommentTimeSep 24th 2017
    Thx for reply. Sounds,like you have two pumps and two "loops". I think I have one circulation loop from store past manifolds through boiler and back to store with one pump. I think I can wire per my original note to achieve the cycle you outline. Wiring centre activates pump and thermostat turns boiler on when temp drops in tank. However, I need to ensure Pump is always on when Boiler is on. Also, because the store also heats the DHW, I also need the pump and boiler to activate from the thermostat when the Wiring Centre is not calling for heat.
    • CommentAuthorCaterham07
    • CommentTimeSep 25th 2017
    Been thinking about helpful comments from Mattstan51 and CWatters. I have been assuming I have one circulation loops but perhaps I have two. I have two output pipes at either side of the top of the store and two returns at the bottom. The circulation pump is on one of the top outflow pipes. When the pump is on, both outflow pipes heat up as do both returns. I can see five pipes going into the wall, 2 x boiler, 2 x UFH and I to the expansion vessels that are in another location ? One outflow pipe has the pump, perhaps it is pressure in the store that creates circulation in the other loop. If I assume the pumped outflow is to the Boiler, the other outflow should be to Manifolds ? The non pumped side has valves that I can close and test whether the manifolds stay cold. My solution could be that a second pump on the non pumped outflow controlled by the wiring centre will avoid conflict at a single pump.
    Posted By: Caterham07If I assume the pumped outflow is to the Boiler,

    You can't assume!! you need to find out.
    One pump can create flows and back flows on unrelated but connected loops.
    Lots of boilers have circulation pumps incorporated within them, check your boiler for this.
    IMO you can not solve this problem by fiddling with the control circuitry.

    The way thermal stores work is that the heat source (boiler, solar etc.) heats the TS and the TS supplies the heat load (DHW or/and CH) The two circuits, supply and load, should be independent of each other.

    So you should have a pumped circuit from boiler to TS (gravity with a (modern?) oil boiler probably won't be an option) and a pumped circuit from the TS to the load. Sometimes there is more than one pump on the load side depending upon the requirements and sometimes the additional pump(s) are replaced by motorised valves.

    Each pumped circuit will need a non-return valve (usually located at the pump) to prevent back flows and interference from other pumped circuits. I suspect that you may be short of a couple of strategicly placed non-return valves!
    • CommentAuthorCaterham07
    • CommentTimeSep 25th 2017
    Should say the 'assuming' is because the house is five hours away. Agree that there is a Pump missing on the load side and adding this and connecting to the Wiring Centres should resolve the issue. Going to check the details this weekend at the house and then sourcing a plumber. Thx for your time and help.
    But you will need non-return valves in both the boiler and heating loops otherwise back flows will cause all sorts of issues. I would be surprised if the system was installed without pumps on both boiler and load loops but I could imagine non-return valves being omitted.
    • CommentAuthorCaterham07
    • CommentTimeSep 26th 2017
    Noted and thank you. I have spoken to the UFH system designer now and the problem is that the plumbing for the store was installed with only pump instead of the required two. I assume that non return valves may not be right either as you say. The designer has also suggested that the couplings being used should be reviewed (may start another thread on that). With the help of the forum I have got to the issue, just need to find a plumber now ... thank you.
    • CommentAuthorborpin
    • CommentTimeOct 2nd 2017
    Several things as I have a similar setup.

    Firstly the water in the tank is both heated by the boiler and used for the UFH. If you have a system boiler, it has a builtin pump else you need a separate pump. the control of the temperature of the tank should be independent of the heating or DHW so the tank thermostat just drives the boiler and the associated pump.

    Secondly, these tanks should have a blending valve on the UFH output side so it pulls the heat from the bottom first then progressively higher up. If you do not have this valve you need it to maximise the draw from the tank.

    Finally you should have a dump valve that makes sure the flow to the boiler is always about 40Deg.

    If you lok at this diagram you will see both valves. http://www.akvaterm.fi/eng/Accumulators/AKVA_SOLAR.41.html

    So yes you need 2 pumps, one for UFH and one for Boiler. Tank thermostat controls the boiler, room stat controls the UFH pump.
    Thx. I visited the house at the weekend and found that there was second pump fitted within the housing if the external oil boiler. I was able to rewore the UFH to the pump I could see next to the TS and the Boiler and it’s pump to the Ts thermostat. Everything is now working. Thx to all who took the time to respond and help.
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