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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    Wondering if I can pick your brains on a fairly well worn subject.

    I have a solid fuel Rayburn which I rarely use - boiler current removed and replaced with a heat brick. I use an ASHP for heating and hot water. With electric prices, have the feeling I should integrate by Rayburn boiler somehow. I have a sealed system, no thermal store - the ASHP heats UFH and DHW tank directly.

    The floor height of the water tank is approx 1m below the Rayburn floor height. I am wondering about adding a buffer tank somewhere, and then linking that in to the existing system.

    Thoughts appreciated. Since I have the Rayburn, the Rayburn boiler and the existing system - wondering if I can add a few system parts and do this integration.

    • CommentAuthorGreenPaddy
    • CommentTimeJun 17th 2022
    Just a few thoughts, questions:

    - is your HP directly feeding the UFH manifold, and via a coil in the DHW tank?
    - if you rarely use your stove now, are you really going to use it very frequently after doing the conversion work?
    - a buffer tank is a good way to allow a point of integration, but you'd need a lot more than just a buffer tank, eg. header tank (if open vented) pump(s) to feed from the boiler stove to the buffer tank (if not grav) and from the buffer tank into the DHW tank (if it has a coil).
    - are you wanting to use the boiler stove water to feed the UFH too?
    - maybe you set the buffer tank beside the DHW tank, and just link them? But then you risk having to heat a larger body of DHW with the ASHP.
    - do you have a free/cheap source of seasoned timber?
    - I'm deliberately ignoring the issues around combustion particulates, as that's been covered lots of times previously, and can be searched for if you are concerned.

    My initial reaction is that there would be quite a lot of cost, just to provide a proportion of your hot water. Those costs come with their own carbon footprint, not just a dent in your bank account. Maybe just run the stove more, as a stove, and let it do the space heating.
    Hi GreenPaddy,

    Thanks for your thoughts/questions.
    I do have low cost seasoned timber which is why I was considering this as a viable option.

    The HP does feed the UFH manifold directly and via coil in DHW tank. I was thinking if I did this that I would perhaps modify complete setup, so that UFH could avail of the cheap additional heat from the Rayburn. I know it would cost some money, but thinking the payback might be pretty quick with the current electricity prices.

    My COP average over the last 3 years is about 2.7, which I am not very impressed with. Its an 8 year old system, so perhaps technology has moved on! The system uses compensation curve, and I have turned down the flow temperature range to try and increase the COP, but it has made very little difference to the COP.

    Maybe another option could be to just ad a couple of radiators off the Rayburn supply for space heating and forget about the hot water side?
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