Author Topic: Hot Water System Upgrade Ideas  (Read 466 times)

Hot Water System Upgrade Ideas
« on: November 23, 2019, 03:15:05 pm »
In my cottage, I'm looking for possible ways to upgrade the existing HW system.  I am restricted to a traditional vented system because I'm not connected to mains water, so water is pumped from a well to a header tank.

Existing System
A traditional vented indirect hot water cylinder in a gravity-fed HW system is heated by a solar water heating array (currently defunct), or by an immersion heater. No mains water available, so system header tank is fed by well pump with electronic control via float switches.

Proposed System
Retaining the gravity-fed HW system design (and well water pump supply), it is proposed to fit an upgraded open-vented thermal store, with an indirect heating coil, with motorised valve switching to switch between input from a wood-burning stove and a solar water heating array (whichever provides the most heat at any one time).  The store will have a supplementary immersion heater.  The system should provide hot water for kitchen sink, 3 x basins and 1 shower, and underfloor heating for an area of max 15 sq.metres.   

My main question is whether it is possible to supply DHW and water underfloor heating from the same thermal store, as DHW would be, I guess, 65deg, whereas underfloor heating might be ?20deg?.  Is it possible and how would it be achieved?  Has anyone done anything similar?

Re: Hot Water System Upgrade Ideas
« Reply #1 on: November 23, 2019, 03:23:07 pm »
Pcolbeck OTP has a heat store system similar to what you are proposing I think.  Drop him a pm.
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Re: Hot Water System Upgrade Ideas
« Reply #2 on: November 23, 2019, 03:38:04 pm »
Thanks.  I've sent a PM.

Re: Hot Water System Upgrade Ideas
« Reply #3 on: November 23, 2019, 09:24:51 pm »
It's a good idea to have a system where you can pre-heat the hot water with solar/the wood burner, and then top up the heat with an immersion heater. That is often done by having the immersion heater near the top of the tank, with the bottom of the tank heated by the solar/wood burner. It can also be done by feeding water through a tank heated by the solar/wood burner then a tank heated with an immersion heater.

The reason for that is that if you just have one tank, all of which is heated by any heat source, when it is heated hot enough to use,  the solar/wood burner will be less effective or have nowhere to put heat.

You can run the underfloor and the DHW from one tank. The water in underfloor heating will be a bit hotter than 20 deg, but the temperature for that can be limited with a thermostatic mixing valve.
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Re: Hot Water System Upgrade Ideas
« Reply #4 on: November 23, 2019, 10:44:53 pm »
Do you have mains gas or access to LPG?

Or do you have the space for a ground source heat pump.

These are going to be expensive to install.

Re: Hot Water System Upgrade Ideas
« Reply #5 on: November 23, 2019, 11:03:52 pm »
Do you have mains gas or access to LPG?

Or do you have the space for a ground source heat pump.

These are going to be expensive to install.

No mains gas, but access to LPG.

Yes, there's space for a ground source heat pump, but don't think I could afford that without extensive borrowing.

Re: Hot Water System Upgrade Ideas
« Reply #6 on: November 24, 2019, 10:12:58 am »
Double check the RHI and financing options to fund the ground source heat pumps.


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Re: Hot Water System Upgrade Ideas
« Reply #7 on: November 24, 2019, 10:38:55 am »
Regarding under floor heating... As I recall, the input to the underfloor heating system is usually temperature controlled with eg: a themostatic head unit measuring the temperature of the underfloor supply - it can take any temperature water from 20C to 70C (in our case about 65-70C) but trickles just enough through to keep the temperature in the under floor pipes at the right temperature. The wall thermostat simply switches the whole lot on or off as needed - you can build in (a little) intelligence into the wall thermostat circuit to cope with the huge hysteresis caused by the very slow heating response time. I vaguely remember building simple circuits to do this many years ago at Uni (analogue integration and differentiation) to control laggy systems using a couple of (new at the time) operational amplifiers to control a relay switch.

Re: Hot Water System Upgrade Ideas
« Reply #8 on: November 24, 2019, 10:43:52 am »
Thank you all for all of these interesting ideas.

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Re: Hot Water System Upgrade Ideas
« Reply #9 on: November 24, 2019, 08:21:32 pm »
A bit of specialist knowledge possibly irrelevant in your case: underfloor heating wrecks pianos. You can buy some sort of blanket to put underneath a piano to protect it from directly rising warm air.
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Re: Hot Water System Upgrade Ideas
« Reply #10 on: November 24, 2019, 10:42:30 pm »
Thankfully, no pianos in danger in this case...

Re: Hot Water System Upgrade Ideas
« Reply #11 on: November 24, 2019, 10:56:11 pm »
Hot water stores with plate heat exchangers for dhw and ufh circulation are a 'Thing' albiet quite a  pricey thing.