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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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  1.  
    Can anybody help me with where I can connect an air source heat pump to my heat store? I'm short of ports, so I was wondering if I could use the ports that connect to the UFH (of which there are 3, top, middle, and bottom). I'd really appreciate any advice on what might be possible.
    • CommentAuthorGreenPaddy
    • CommentTimeMay 17th 2020
     
    Without seeing all the detail of your system...I often design TS's with dual connections (ie using one connxn to do two things). It's not a bad idea at all to have the flow from the ASHP T'd with the flow to the UFH. Likewise the the return to the ASHP T'd with the return from the UFH.
    The flow directions are opposing, so you won't get a restriction at the connxn point. Also, you'll get less flow through the TS, when both ASHP and UFH are running, which will help reduce destratification inside the TS.
    Does your ASHP have 2 seperate flow pipes (one for high temp DHW, and one for low temp heating), or just one flow pipe? Ideally you would feed the high temp flow from the ASHP to the top of the TS.
    If you do have just one flow pipe from the ASHP, adding a couple of 2ports or a 3port valve would let you split the high/low temp flows.
  2.  
    Thanks @GreenPaddy, that's really helpful.

    The ASHP that I'm thinking of buying is just a simple one with two pipes, so I was thinking of splitting these so that I can either heat the bottom part of the store or the top part of the store. Presumably I can do this with 4 ports and 2x 3-way valves, or 1x 6-way valve? Or ideally with 3 ports so that it can go through bottom>middle or middle>top. Not sure how I'd connect the valves to achieve this though.
    • CommentAuthorGreenPaddy
    • CommentTimeMay 17th 2020
     
    Something like this would do what your after. I perfer 2ports rather than 3 ports... see sketch
    • CommentAuthorGreenPaddy
    • CommentTimeMay 17th 2020
     
    Just re-read your OP. It seems you have 3 UFH connxns on the TS (top mid bott) is that correct? Not sure why you would ever feed UFH from the top of a TS?

    My sketch assumes 2 TS connxns for UFH (mid and bottom).
  3.  
    Hi @GreenPaddy, sorry if I wasn't clear! I was assuming 4 connections initially, but that doesn't make sense as you can achieve the same with 3 - as your sketch shows. That's exactly what I needed! Thank you. So when tank cool, takes from middle, returns to top. When tank warm, takes from bottom, returns to middle.
  4.  
    And yes, we have 3 ports for UFH. Top mixes in, so you'd never take 100% from the top, but I guess it can contribute if the middle isn't quite hot enough.
  5.  
    Do you draw DHW from this heat store? (via coil/heatx)? If so, I wouldn't normally have a UFH draw from the top, in order to protect the top for DHW. If it's purely a heat store for space heating, (buffer tank), then fine.
    • CommentAuthorborpin
    • CommentTime3 days ago
     
    When you plumb it in, fit a flow meter and some temperature probe pockets. You are bound to want to find out when it is flowing an the temperatures at a later point in time! Yes it will have them built in, but can your custom control system read the data (when you want to use it).
  6.  
    Posted By: GreenPaddyDo you draw DHW from this heat store? (via coil/heatx)? If so, I wouldn't normally have a UFH draw from the top, in order to protect the top for DHW. If it's purely a heat store for space heating, (buffer tank), then fine.

    Yes, it's also used for DHW. I doubt we'd ever want to draw from the top. Normally it just mixes in a small amount from the middle. Only if you wanted the UFH to be really hot, or if the whole store was extremely cool would we draw from the top. But as that's how it's plumbed already, I don't think it's a problem.
  7.  
    Posted By: GreenPaddySomething like this would do what your after. I perfer 2ports rather than 3 ports... see sketch


    I assume this uses 4 open/closed valves. Is there a way of doing it with 2 x 3-way valves?
  8.  
    Something like this?
      IMG_20200523_225321 (1).jpg
    • CommentAuthorEd Davies
    • CommentTime2 days ago
     
    I have a notion in the back on my brain that 3-port valves can't be used with the water flowing through them the “wrong” way (i.e., from A or B to AB) - to do with the pressure/flow pushing the actual valve bit one way or the other. Is that right?
  9.  
    Posted By: Ed DaviesI have a notion in the back on my brain that 3-port valves can't be used with the water flowing through them the “wrong” way (i.e., from A or B to AB) - to do with the pressure/flow pushing the actual valve bit one way or the other. Is that right?

    Good point. It might depend on the valve. The ESBE 3-day divert valves that I'm familiar with seem to be indistinguishable inside, so I don't see why they couldn't flow either way. I'll check though.
  10.  
    Eg, the ESBE VRG130 series seems to be capable or mixing or diverting.
  11.  
    Looking at the circuit above again, it looks like the top 3-way valve only works as a divert valve, and the bottom only as a mixer valve, so the flow will always be the same way through each valve.
    • CommentAuthorEd Davies
    • CommentTime1 day ago
     
    Indeed, but my understanding is that most standard 3-port valves don't work as mixers, only as diverters. I think it's to do with them relying on the pressure to help hold the valve in position. With the flow in the opposite direction the pressure tends to push whichever valve is supposed to be closed open.

    Maybe in an application like this you could get away with it because the pressures from the two connection points on the tank would be so close (+/- the different heads which would cancel out, of course) so long as you kept the pressure drop in the pipe with water flowing in it to a minimum. Dunno. Is there a plumber in the house?
  12.  
    Posted By: Ed DaviesIndeed, but my understanding is that most standard 3-port valves don't work as mixers, only as diverters. I think it's to do with them relying on the pressure to help hold the valve in position. With the flow in the opposite direction the pressure tends to push whichever valve is supposed to be closed open.

    The ESBE 130 series valves can definitely work as either mixer or diverter valves, but I accept that other valves may not.
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