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Author Topic: air to water ashp  (Read 2648 times)
JonG
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« Reply #30 on: July 22, 2017, 06:21:45 PM »

It comes down to the pressure drop which has to be considered and can be calculated, but in most scenarios using a rule of thumb for the heat carrying capacity of the pipe is sufficient. This gives you the required flow rate (lpm/lps/m3h), the velocity also has to be considered (m/s) and this is generally kept as close to 0.9 m/s as possible to avoid noise and erosion.

If you need multiple pumps or hydraulic separation then the velocity needs to be reduced in a header or buffer but that is probably out of scope of the OP. In order to achieve what you want you want the correct flow rate, and a pressure drop low enough to work with the duty of the pump at the required flow rate.

It can all be calculated out but generally copper is a better choice than plastic, due to the lack of inserts which increase pressure drop and smaller internal diameter, which increases linear friction.

We are starting to see more issues with plastic too, in terms of water quality. This is thought to be because the fittings have no barrier against oxygen entrainment, and where a plastic fitting joints copper to plastic the dissimilar coefficients of expansion and contraction may result in ingress at the o-ring. These are just hypotheses at the moment.

We now wont use it on heating circs and only use copper or MLCP.


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eabadger
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« Reply #31 on: July 23, 2017, 09:18:08 AM »

i have always used the specific barrier type pipe for heating, which i understand has an oxygen barrier, i tend to use hep20 either blue stripe no barrier for fresh water and red stripe for heating, with tails in speedfit as white, all inserts superseal and have had no issue.
all backboiler pipe in 28mm copper with hard brazed joints (rules here).
more than happy to pipe it all in copper and will to test out, our saying is "its all a big experiment", my logic tells me that the exit of heat pump an entry of cylinder will be the limiter, but happy to be wrong.

what is MI? manufactures instructions? if yes i will post on here.
yes the gauge i was referring to was the refrigerant pressure, hence comment that it appears to have slightly too much at rest .2mpa more than instructions state.
also what i have read, the initial gas should be (on high end units) be set onsite and calculated for local weather.
i dont understand why max mpa on my air to air pump is higher on the same gas? assume manufacturing differences.


what i have done last night is to open the manifold to the 5 x towel radiators, could not do last week as was so hot, yesterday afternoon was pretty miserable weather, so not a conclusive test as outside temperature was cooler, water in cylinder topped out at 51*

again dont get me wrong, so far very happy with the heat pump, only time will tell as to how long it will last, but looks ok and is far quieter than i thought it would be, the dogs loved it in the hot weather, they lay down with the cold air blowing over them!
on that point why not duct the cold air back in to the house to cool it? possible?

steve

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1600w PV main array at 24v, excide 2v 1000a forklift cells now x 2, 320w PV secondary array at 12v. Enfield 1944 ex RAF 5.6kw diesel genset (now in pieces, big ends gone), Petter AC1 28v diesel charging set at 2.8kw.
1kw wind turbine.
26kw wood stove back boiler to underfloor heating and dhw
JonG
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« Reply #32 on: July 23, 2017, 04:20:38 PM »

How are you avoiding an HP trip when the wood burning stove is lit and contributing?
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eabadger
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« Reply #33 on: July 23, 2017, 05:20:20 PM »

one of the sensor on wood burner closes zone valve and locks out the heat pump, why?
28mm two port valve n/o is powered shut when heat pump is on.

steve
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1600w PV main array at 24v, excide 2v 1000a forklift cells now x 2, 320w PV secondary array at 12v. Enfield 1944 ex RAF 5.6kw diesel genset (now in pieces, big ends gone), Petter AC1 28v diesel charging set at 2.8kw.
1kw wind turbine.
26kw wood stove back boiler to underfloor heating and dhw
JonG
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« Reply #34 on: July 23, 2017, 06:11:24 PM »

Same principle really if the heat pump circulates water at WBS temps through its plate while the compressor is running the fridge temps can rise and trip the HP stat. If the signal is simply 230 v off the 2-port without some form of hysteresis this may be an issue.

If you upload a schematic happy to have a look for you.

We had a GSHP with a PV array also heating the cyl, and periodically the high temps in the cyl would result in a hot slug which tripped the HP stat, so ended up capping the PV immersion temps. With a WBS unless you are feeding out of a buffer through a mixer more of a potential issue.
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eabadger
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« Reply #35 on: July 24, 2017, 08:07:34 AM »

hello, it is the pressure causing the error and not a stat at high temp, admittedly the temp does change the pressure.
we dont intend to use both at the same time, our wood boiler is a 25kw to water and does all our dhw and heating good hardwood ranges from cheap to free here, collecting a corde of dry oak for 100 this week Smiley, the heat pump is for water heating when not wood burning season, i have added the automation to stop a mistake, so if temp of the gravity up pipe of the back boiler is above 40* the heat pump is shutdown and locked out at which time the normally closed zone valve shuts isolating it.
same sort of principal with wood boiler, when heat pump is on it drives a normally open valve shut on the pumped side of the wood burner, to stop the wood burner being a radiator in the summer, the back boiler is a 4 port type, two cross linked on pumped side and others for unobstructed no matter what gravity feed to two 3kw rads.


back to the heat pump, i tried something different yesterday, parameter for max water temp is 55* default parameter for water return is 45* but on a dutch website of a very similar looking unit both theses temps are 50*, so tried it that seemed to make a positive difference, only time will tell as weather not the best currently, but water topped out last night at 53* with no trip outs.

i can do a pipe layout schematic in as far as a fag packet sketch?

steve
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1600w PV main array at 24v, excide 2v 1000a forklift cells now x 2, 320w PV secondary array at 12v. Enfield 1944 ex RAF 5.6kw diesel genset (now in pieces, big ends gone), Petter AC1 28v diesel charging set at 2.8kw.
1kw wind turbine.
26kw wood stove back boiler to underfloor heating and dhw
eabadger
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« Reply #36 on: July 29, 2017, 11:19:47 AM »

bit of an update, changed the modulating pump for a grudfoss standard 3 speed one, made a slight difference, but having taken some advice i checked the eev setting which is the expansion valve, on these pumps it appears the eev times down to create more pressure, it seems the default 35 setting was increasing pressure too soon, changing this setting to 40 has stopped the problem, i am going to re pipe as suggested in 28mm copper and set eev back to 35 to see.

any advice from those in the hvac trade on the setup of initial eev setting appreciated, i read the hitachi manual for a similar hp that suggested the setting was based on environment and charge of gas, wet and dry bulb measuring which went over my head, simple explanation?


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1600w PV main array at 24v, excide 2v 1000a forklift cells now x 2, 320w PV secondary array at 12v. Enfield 1944 ex RAF 5.6kw diesel genset (now in pieces, big ends gone), Petter AC1 28v diesel charging set at 2.8kw.
1kw wind turbine.
26kw wood stove back boiler to underfloor heating and dhw
eabadger
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« Reply #37 on: September 12, 2017, 05:19:47 PM »

ok, another update, re-piped in 28mm copper, sloping bends, no difference.
however biggest difference was changing pump from return as shown in the manual to the flow, works a treat now, just in time for wood burning season. Sad
but hope to use the ashp for floor heating, tried yesterday and very happy with results, so new plan is if generator needed in the autum winter months we can pre charge floor at same time as charging batteries.
also got my second battery bank set up with a manual changeover switch to the ashp supply, i can heat the dhw for 3 days if need be, then switch back and leave the spare battery to re-charge.

steve
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1600w PV main array at 24v, excide 2v 1000a forklift cells now x 2, 320w PV secondary array at 12v. Enfield 1944 ex RAF 5.6kw diesel genset (now in pieces, big ends gone), Petter AC1 28v diesel charging set at 2.8kw.
1kw wind turbine.
26kw wood stove back boiler to underfloor heating and dhw
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