Results 51 to 85 of 85
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18-09-2011, 01:37 AM #51
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Gary, it about the water flow through the heat pump and control of the water in the storage cylinders.
On a one pass system (where water leaving the heat pump at a very high temp) then you are correct, however very high outlet temps mean permanent high discharge pressures, and lower efficiency. How ever if you for a full circulation system, where the heat pump only increase the temp of the flow by a few degree's per pass, the discharge pressure are kept low for longer periods. (only at the end is the discharge pressure high) for this to cylinder heat ex-changers must always bee in the coldest part of the system (I do not use internal heat ex-changers, I pump from the cylinder through a heat ex-changer and back again returned at low level)
It is all down to flow, heat transfer and available duties. You have to look at the whole application and the influences of each part of the system. What is installed is a boiler system!
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18-09-2011, 02:55 AM #52
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Yonatanb,
I am familiar with codes in a few countries and I do a lot of solar so Israel was always a model for us in North America, to no avail, as it is not mandated in any code here. I know the Chromagen product and the HX is in the bottom 2/3 of the tank.
I assume the fittings are 3/4" or equivalent so there is not much HX area in one tank. The pressure drop is too high for all three in series and the usefullness of the last tank is suspect. Put them in parallel. You will have a huge increase in performance. The HX is only 1.2m2 per tank which would be good for about 6kw each when the dT is 20C. I don't think you can get the performance from the tanks with such a small dT. You need to get a higher flow through each HX and with the current arrangement you will not get much more.
Mad is right, as this system is similar to a solar system except the dT is a lot smaller than we would have with solar. The tanks were designed for solar.
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18-09-2011, 03:05 AM #53
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Last edited by Gary; 18-09-2011 at 03:16 AM.
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18-09-2011, 03:23 AM #54
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
I'm going to bed....Long day today
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18-09-2011, 05:58 AM #55
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
A long read. Can someone summarise why, with dedicated circulation pumps, the heatpump thermostat keeps telling the unit to re-engage, in such short time intervals?
Where is the temp probe actually measuring at the moment?
Where is the OP going to move it (temp probe) in future developments?Last edited by desA; 18-09-2011 at 06:03 AM.
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18-09-2011, 08:46 AM #56
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Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Last edited by nike123; 18-09-2011 at 09:04 AM.
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18-09-2011, 09:24 AM #57
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Re: Frequent compressor cycling when using a ASHP for shower water heating alone
This pipe and electrical heater setup on improvised stand is looking strange to me, and it looks more like this tank should be mounted horizontally.
Could OP give more details of make and model of this tanks?Last edited by nike123; 18-09-2011 at 09:34 AM.
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18-09-2011, 10:48 AM #58
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
@ desA:
The heatpump operation is triggered by an internal sensor at the output of the heatpump. All the readings I previously provided are taken from this output sensor. I can also monitor the temperature in the inlet of the heatpump if required.
The local expert does not rule out any of your suggestions, but he would like to follow his debugging procedure, which includes replacing the two water pumps with a single centrifugal water pump.
after the problem is solved, one way or the other, i will summarize everything, and post the the summary so all of the experts here could draw final conclusions.
@nike123:
Thank you for your comments !
you are correct. the labels on the tanks indicate both horizontal and vertical operation is possible.
70L of hot water per shower/bath is a gross exaggeration in a country where 10,800,000 inhabitants occupy ~28,000 [km^2], most of which is defined as a desert (==annual precipitation is less than 200mm). the government here has actually installed water savers on each faucet (either in shower or in the kitchen). anyways, taking short showers is part of the basic training here.
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18-09-2011, 10:51 AM #59
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
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18-09-2011, 10:52 AM #60
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Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Any detail on manufacture of tanks and model of tanks?
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18-09-2011, 10:58 AM #61
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
@nike123:
nothing more than the details specified in reply to an earlier comment by MikeHolm.
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18-09-2011, 11:11 AM #62
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
@desA:
The sensors are hidden under the hood, which i do not want to take off due to warranty issues. In case my cyber presence is tolerable, i promise to update this forum with any development.
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18-09-2011, 11:12 AM #63
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
This is what is going to happen! New pump "all Ok now mate"
What is really going to happen, increase set off set point, increase differential (lowers "cut in" point) increase anti-cycle timer just in case. No short cycling now.
The facts are!
Not enough surface area in your cylinders (regardless of the configuration)
DesA is an expert on heat transfer, what would you expect the entering water temp to be, passing through 1" 12m long spiral tube inside a static cylinder, if the water in the cylinder is 45C to deliver 6kw of energy?Last edited by mad fridgie; 18-09-2011 at 11:49 AM.
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18-09-2011, 11:25 AM #64
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
@mad fridgie:
you are my guardian angle! i will closely monitor all the parameters you have kindly provided. additionaly, i will closely monitor the CoP.
other than that, the heat exchanger spiral in each tank is 12[m] (about 40 ft.) long, not 1.2[m].
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18-09-2011, 11:26 AM #65
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
that is "angel". :-)
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18-09-2011, 11:28 AM #66
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Re: Frequent compressor cycling when using a ASHP for shower water heating alone
I see 3 pipes are comming at bottom of cylinder and 1 pipe at side of tank. One connection is blanked.
Middle tank have side outputs which are different in position than other two.
I think we should first confirm that tanks are connected as it should be regarding inlets and outlets.
I think that parallel tanks configuration is better one, but it must be balanced.
Since heat pump works with temperature difference of 5K to 8K at maximum, heat exchanger surface of tank which is made for 10K (or more) differential is to small to transfer effectively heat to water in tank and therefore you experience frequent compressor starts and short running time.
In paralel (balanced) setup, same energy is disipated from 3 times bigger surface and you should have better heat transfer to water in tanks and your heat pump temperature diferential should drop to 5K.
Could you take picture clearly of labels on tanks and translate to english what is written there?Last edited by nike123; 18-09-2011 at 11:32 AM.
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18-09-2011, 11:35 AM #67
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Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Below "Ideal" what is written on Hebrew?
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18-09-2011, 11:55 AM #68
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
In Toronto, We have set up hot water meters on 100 houses as a test to see what the average shower length is and how much water was used with different shower heads and under pressures which vary from 3-4bar (typical for Toronto). From my own experience, my normal 5min shower is using 25-28L but I am not a teenage kid and don't do 30min showers. The range in the 100 houses was from 20-80L so it is hard to get a concise figure.
We are also heating from 5-8C to 50C typical.
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18-09-2011, 11:57 AM #69
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18-09-2011, 12:10 PM #70
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Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Also, by looking of how is piping done and stands for tanks, that is some "hack of the year".
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18-09-2011, 12:21 PM #71
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
@MikeHolm:
i think Mad Fridgie referred to the length, and i gave the figure i was handed by the installer. you are right of course regarding the Chromagem tank spec. and regarding the postulates of physics.
instead of feeding you with partial/incorrect/irrelevant data, i contacted the tank supplier for details, and hopefully, he will send me some kind of a spec sheet with actual drawings. since most of the suppliers here religiously believe in the "buy & go (to hell)" principle, i can only hope for a miracle (isn't the holy land a fine place to do so ? :-).
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18-09-2011, 12:29 PM #72
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
@nike123:
A. by "piping" you refer to the design or the physical connections?
B. what is wrong with the stands and how does it affect the system's performance?
i will call it a day. thank you again!
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18-09-2011, 12:41 PM #73
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Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Nope. I refer to layout of pipes, not design. This is not the work of professional.
This is work of "take money and run fast and far as possible" "professional".
B. what is wrong with the stands and how does it affect the system's performance?
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18-09-2011, 03:00 PM #74
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Last edited by Gary; 18-09-2011 at 03:05 PM.
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18-09-2011, 05:20 PM #75
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Mads way of piping is fine, just remember to have the "header pipe" at least one size larger than the pipes from the tanks. In this way, the pressure on each tee going to each tank will be equal and you will get equal flow through the tanks. This applies to both the DHW piping and the HP piping.
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18-09-2011, 06:18 PM #76
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Last edited by desA; 18-09-2011 at 06:59 PM.
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18-09-2011, 10:27 PM #77
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Firstly apologies, the heat exchangers are indeed 1.2 square meters!
I have re-read the thread.
Water use 700L form say 20C water in to max water out 55C, 28.5kwkr/24hrs
That is about 25L/person (remember that the hot is mixed with cold to give the shower head flow) and that would seem about right.
You will have losses from cylinders (2kw per cylinder) total 6kwhr/24hrs.
So the max amount of heat required is roughly 34.5kwhrs/24hrs.
Power used is 17kwhrs/24hrs that a COP of 2, and that is shocking especially in the ambient temperature range.
It is very clear that the installer has no clue what he/they are doing. (well they know how to make a bob or 2)
So the fix and some money back!
A; get them to rip it out completely and get a full refund (unlikely to happen)
B; Re plumb the cylinders as shown "in parallel", ( I would normally get rid of the buffer tank, but as they have no clue best leave in as a low loss header, leaving in 2 pumps one for heat pump and one for the cylinders), replace the whopping big 18Kw unit, and replace it with a 3-5Kw heat pump unit. Control the heat pump directly or indirectly by the storage cylinders temperature (sensor 1/2 way up the cylinder). turning off the water pumps when heat pump is not in operation.
You require at least 0.5l/s going through the heat pump, and at least 0.5L/s going through each cylinder heat ex-changer (1.5L/s total)
I would have the cylinder stat set at low 50Cs cut out, and 40C cut in. The internals of the heat pump cut out as safety at 58C (return water temp).
This will give a reasonable balance between heat pump, heat exchangers, use and give you great COPs ( i would expect the COP to between 4 and 5, or power usage around 7-9kwhrs/day)
"Then ask for a refund on the price difference between the units"
PS: I do not agree with coils in cylinders for heat pump applications!Last edited by mad fridgie; 18-09-2011 at 10:57 PM.
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19-09-2011, 11:50 AM #78
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Mad, the problem here is that, even if the system is piped perfectly, I fear that the total HX area is less than half than it should be for the desired heat transfer. You will not get the same heat transfer from an immersion coil that you will get with a system pumped both sides.
That said, if the OP used 3 Viessmann tanks with 2.0m2 surface area, piped correctly, the performance would be drastically different. The problem lies in that with the small deltaT, each of the current HX is good for, I think, at best 4kw so with 18kw to play with...............................ain't gonna happen.
Yonatanb, ask Mad to draw you a diagram with an external HX and I will look at the tank drawing to see if we can use the existing ports on the tanks to pipe it in. In this way we may be able to give a much better performance.
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19-09-2011, 12:02 PM #79
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
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19-09-2011, 12:45 PM #80
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
As desirable as it may be to rip it all out (18kw is a lot for this application), It may not be in the budget to go to that expense. I think the tanks can be retrofitted to act as storage tanks without the HX and at least he can salvage the basic equipment. If he has room, he may be able to add one more tank if need be.
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19-09-2011, 08:47 PM #81
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
I am under the impression that this a new system, so the expense should be borne by the installer, and even giving a refund for down sizing the unit. (well that is what would happen here in NZ), How ever we are not sure what instructions were given by the client.
If no major change can be made, then yes get rid of the internal heat ex-changers and go external PHE.
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19-09-2011, 09:26 PM #82
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Some contractors give the bumper to bumper warranty or "if you can see my bumper, you have a warranty". Don't know if that is the case here.
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20-09-2011, 06:14 AM #83
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Gary mentioned:
It sounds to me like the heat pump sensor is attached to the outgoing water pipe, instead of the incoming water pipe.Engineering Specialist - Cuprobraze, Nocolok, CD Technology
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20-09-2011, 06:18 AM #84
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
Additional points.
Where does the cold air exiting the ASHP go?
If it is into the room where the hot water cylinders are located, then their heat loss may be considerably more than the 2kW/24h per cylinder, mentioned by MF.
Does this air re-circulate back to the air inlet of the ASHP?
Where on earth is the condensate drain pipe? The floor under the ASHP looks to be covered in condensate.Engineering Specialist - Cuprobraze, Nocolok, CD Technology
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20-09-2011, 11:43 AM #85
Re: Frequent compressor cycling when using a ASHP for shower water heating alone
It does indeed look as though the air off is into the room but there seems to be no door on the room so extra heat loss may be there.
A big issue is the line sizes to the tanks, looks like 16mm rubber hose, does not promote good flow.
There may be a floor drain right under the HP, I should hope so.