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Discuss Intergrating stove ,solar thermal and ground source heat pump. in the Renewable Energy area at

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  1. Norcs

    Norcs Member

    None of those schematics represent the viessman and kensa "series" connection design.
    Because they fit the buffer on the by pass loop and fit stats at the top and bottom of the buffer. (kensa fit a 0.4 bar by-pass valve)
    So their buffer is heated from the top down and cooled from the bottom up. Ideal for twin stats operation and eradicating cycling.
    Its a shame kiwa didn't run that test.
    The engineers at viessman are no slouches. Kensa copied their design as viessman were using it decades ago.

    And of course as the buffer is being depleted in the CH any demand from the HW can still be fulfilled by the heat pump.
    Last edited: Nov 25, 2015
  2. Norcs

    Norcs Member

    kiwa state
    "If the required system volume is not available the system should be supplemented by a two pipe buffer tank placed in the return pipe to the heat pump."

    The problem with that statement with its corresponding schematic in fig 26 is that the space heating may be satisfied and the buffer is not recharged fully. So when the system starts again the heat pump just cycles on instead of using stored energy alone as per the viessman design.
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  3. Nostrum

    Nostrum Plumber GSR

    The buffer should always be fully charged at the end of a cycle as the heat pumps set point is based on the buffer / return temperature and not switched by the room stat or similar. Likewise when an emitter circuit draws off some heat, the heat pump is triggered by a drop in buffer/ return temp.

    The buffer on the return in series is purely to increase the total open circuit system volume, with the exception of defrost cycle on air source.
  4. Worcester

    Worcester Plumber

    Not quite...

    What they said was:

    That's a volumiser not a buffer. See their schematics.

    Also fully read my thread on two and four port buffers. There is a shed load more experience out there since that report was published in 2013.

    I still stand by my quote that
    Yes they do have schematics without buffers and permanently open loops in ufh is one way of dealing with it, if you ask them, they will always say that a buffer is best.

    As KIWA point out there is quite a big difference between ASHP and GSHP, most ASHP's are inverter driven so modulate down to 30% or less, most GSHP's are fixed output, on or off, so no modulation,

    Out of interest, which GSHP's are inverter driven / can modulate their output (not twins / cascades that switch on or the other on or off) ?
  5. Worcester

    Worcester Plumber

    Sorry guys, duplicated some of your comments, didn't realise it had popped on to page 2 of the thread !! :)
  6. Worcester

    Worcester Plumber

    Also shame that for the DHW consumption they didn't use the official standard - they exist specifically for this reason.

    Tapping Cycle No.2 from EN 13203-2. Tapping cycles are set daily profiles of hot water draws, including the start times and energy per draw, developed by industry to enable different appliances to be tested with exactly the same hot water load.

    That's the problem with govt appointed consultants - making up their own tests !
    Last edited: Nov 25, 2015
  7. Nostrum

    Nostrum Plumber GSR

    Thermia diplomat inverter, 3 phase only for the minute but single phase is coming.

    You'll see them enter the market in the next 12-18 months from most manufacturers. I've been to Sweden to see thier factory and spoken to some of the head honchos about inverter technology.

    It seems that the only reason they're investing into it is because the likes of Mitsibishi, Samsung etc have forced the market down this route with their air con technology.

    Buffer volumes up to about 200 litres tend not to allow for very efficient stratification, so mixing will occur on a 4 port set up. We've still been advised to use them in this way where hydraulic separation is required, but return in series is favoured.

    Another configuration is a 3 port whereby the flow passes through the buffer in series, but with the addition of a return from buffer if flow rates through emitter circuits drop off.
  8. JonG1

    JonG1 New Member

    Heliotherm and Mastertherm (i think) make fully modulating ground source units. The Heliotherm is very expensive and in tests performs no better in terms of SCOP than high end GSHP's like IDM etc.

    They and IDM are more than happy for you to go direct to screed provided volume and flow rate are available. The reason we started doing 4 pipe buffers at 30l per kw was due to the mixing that occurred in the smaller buffers.

    Over the long haul the impact is probably negligible and so many other factors to take into consideration like location of buffer, type of property, interlock, cyclical rate of downstream controls etc. There is no perfect solution.
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