Green Building Bible, Fourth Edition |
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Posted By: cjardWhen you say baffle, do you mean heat exchanger?
Posted By: cjardIs the tank arranged as two separate tanks one stop the other?
Posted By: cjardASHP will generally provide a flow of water that is 7degrees warmer than what it's fed with
Posted By: cjardI'm almost certain you wouldn't want to shower or bathe at 55 degrees
Posted By: cjardRegards target temps, most ASHP will do 60 as a programmed limit, but you'll notice the rate of warming slow down above 52 ish. You should strive to store water as cool as you can rather than as warm as you can because it's easier for an ASHP to generate and the temperature differential to the ambient is lower resulting in lower losses
Posted By: WillInAberdeenWould that start a pumped circuit going from the lower section, through the ASHP, into the upper section, and *downward through the baffle*? IE mixing the top and bottom sections.
Posted By: WillInAberdeenThe heat pump is going to struggle to get the water to 55degC without an immersion top up, which may be better done separately from the heat pump, IE immersion in the store.
Posted By: WillInAberdeenAm assuming you have ufh that the ashp can run at lowish temperature, drawn from the middle of the store, with a dhw coil or exchanger at the top?
Posted By: WillInAberdeenSo circulate the bottom half of the store through the heat pump, to say 45 deg to feed the ufh without immersioning. The very top of the tank heated by immersion to shower temperature.
Posted By: WillInAberdeenOr even do the immersion heating directly, as a topup instant heater on the fresh water pipe that goes from the store coil to the shower.
Posted By: cjard@Will why run the UFH off the TS when the ASHP will provide a controlled target temperature water feed to run the UFH in nonDHW mode?Very good point!
Posted By: CoPWouldn't an ASHP running at very low efficiency still be more efficient than an immersion?Probably, depending on losses such as defrost cycles, but what I meant was that it's better to heat the ufh water only to a lowish temperature, not to dhw temperature.
Posted By: WillInAberdeenSo then the ufh would be completely separate from the TS. The heat pump would run the UFH directly at a nice low temperature for best efficiency, with weather compensation and the like. The TS would only be used for dhw, with the bottom section pre heated lukewarm by solar and ashp, the top section topped-up to shower temperature by immersion, wbs, ashp@low-efficiency.
Posted By: cjardRe your schematics I think that the extra valves (manual, even) and pipe work necessary to have all your heat sources totally configurable as above/below baffle would be a small cost and allow you to achieve best results by experimentation.
Hi Will - just to clarify - you think it is better to have the ASHP connected to the TS? I'm assuming so as it could provide warmish water - 30º-40º at the lower section that would be perfect for the UFH and also effectively pre-heat for the DHW.
pulling the air through a solar absorberGood idea in principle! But the big fan on an ashp pulls through a huge volume of air, many m3 each minute. The solar absorbers would need to heat that volume of air, but not add to the pressure drop across the ashp, which is designed for free air pressure on its inlet and outlet. So additional (even larger) fans would be needed to move the air through the absorber and duct it to the ashp. The power to run these would be set against the gains from the solar absorber.
Posted By: WillInAberdeenif the air behind the slates gets warmer than room temperature, how about blowing it straight into into the house with a bathroom style fan? If not quite warm enough, use it to take the chill off your basement, it'll reduce heat losses through the floor.
Posted By: WillInAberdeenAn advantage of keeping the ashp central heating circuit separate from the dhw/TS circuit, is that the ashp has clever software for weather compensation, so it would like to be left in charge of deciding what temperature it runs at, it will choose the lowest temperature possible at any time, so maximizing efficiency and reducing numbers of stop-start-defrosts (Ours also had 'load compensation' which was even better IME, but relies on calculation of the difference between CH flow and return, which the TS would spoil).
Posted By: ComeOnPilgrimI've finally finished installing.
I'm experimenting with draining all of the heat out of the TS lower section
Posted By: ComeOnPilgrimI mean that if the ASHP supplies the TS, the TS status around the temperature of the UFH, 35°. I don't think this is most efficient. I was thinking of switching off the ASHP when the TS is up to temperature and letting the UFH drain all the heat out of it. Then when it's cool, switch the ASHP back onto 11 to heat it back up to temperature from cold.
Posted By: Ed DaviesClosest might be