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Re: My first self made EVAP
Hi Mike
when in defrost, I presume the fan is off ?
would it be worth insulating the box the evap sits in ?
also you are going for an angled evap this time, whats the benefit here ?
R's chillerman
(maintenance - get 8 hours for what takes me max 4)
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Re: My first self made EVAP
Yes, the fan is off for defrost, I may use hot solar heated water when available to defrost but we will see. The angled coil will aid in getting rid of liquid during defrost and it means I can mount the unit between the houses when there is only 1.8m of space, without pissing off the neighbour.
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Re: My first self made EVAP
Hi Mike
many ventures all in one here, mate, certainly keep you busy and hopefully fat wallet when finalised
another gremlin you have which warmer climates dont suffer is a drop in specific heat transfer
if looking at -20*c .... glycol mix needs to be to -30*c ..... which I think is roughly 50/50
cp of water is 4.18 where glycol is 2.36 ....... lowering efficiency of the already lower temps, heat transfer
was thinking too that maybe during winter you often get clear skys and low sun as we do here, making your solar systems more available for work, but 'think' I recall you saying panels require +15*c to work well and winter sun is not as strong
certainly got your work cut out here mate, finding the right balance of heat/energy/heat
R's chillerman
Argh ! A thought - what about magnification of the sun onto solar ?
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Re: My first self made EVAP
Nope, the normal hot water panels I use produce good heat in -15C -20C as long as it is sunny, which it often is in the winter but i may only get 30C from the panels and not 70-80C that i would like.
Water/Glycol is 60/40 typical. There are additives that help the freeze/boil characteristics somewhat but you are right, transfer is not great. We are used to it in this business as there is not a lot of option except for system that drainback the water to an inside storage tank when not in use.
All in all, solar does work well but financially, not unless you have some subsidy as you have.
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Re: My first self made EVAP
Hi Mike
thats good, got my +/- round wrong way
you can start fires with a magnifying glass, is this something that can be used to increase heat
or is this something that is already part of a solar panel (built in)
seems strange how some western countries subsidise some products and not others
R's chillerman
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Re: My first self made EVAP
I had a lot of t-stat and pump wiring to do before I started up the HP. Yesterday started it up for the first time with a floor heating load, got very high pressures for the first couple of minutes (tank was cold too???) then it settled down but pressure is getting near 400psi at 40C water temp and TXV is hunting a bit. I think I will put in a receiver tank if it will help the hunting issue. I really want something to keep the the pressure from passing the 400psi mark but I'm not sure what the best method should be...any ideas?
superheat is running between 15-16F with a cold tank and 6F when it is near setpoint. DT on the water side in and out of the tank is about 4-5F
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Re: My first self made EVAP
Hi Mike
if valve hunting, first confirm you have liquid feed by taking discharge pressure and convert to saturated temp, then check you have a lower temp on liquid line, if sure you have liquid feed then its just a case of getting the valve set up right
you can increase discharge temp by increasing suction superheat, this will then give you a higher discharge temp at a lower pressure but on the flip side higher suction superheat will reduce mass and compressor work is increased to move the same mass ...
what refrigerant are you using ? R410a for instance has high pressures but lower temp to pressure than other common refrigerants
400psi is 27.2 bar which if R410a is fine
R's chillerman
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Re: My first self made EVAP
Thanks CM, I will look at it again during the week.
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Re: My first self made EVAP
Ignore the fact you have low discharge temps from cold. Its always the case when starting a heat pump. Only when the floors return water temp is 20C plus can you really zero in on whats happening in the fridge circuit.
Starting the machine in cold weather you should actually help your discharge temps by slowing the pump speed until return is about 20C.
What gas are you running. 407C i assume? 400psi is pretty high in that case. What are your inlet outlet temps across HX on water side?
I would install a receiver. Just to give yourself a bit of leeway when it comes to refrigerant charge.
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Re: My first self made EVAP
HI BF, it is a 410 machine but I will have to go back and take measurements tomorrow. Problem is that I am only running on stage one as i haven't put a 2nd stage switch on it yet and I am wondering what the best way would be to do that. Like I said above, I'm getting 10.5A @230VAC on stage one and this seems a bit high to me.
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Re: My first self made EVAP
Quote:
Originally Posted by
MikeHolm
HI BF, it is a 410 machine but I will have to go back and take measurements tomorrow. Problem is that I am only running on stage one as i haven't put a 2nd stage switch on it yet and I am wondering what the best way would be to do that. Like I said above, I'm getting 10.5A @230VAC on stage one and this seems a bit high to me.
If its 410a then you're not a million miles out at 400psi. Your condensing temp should be about the same as your outlet temp give or take a degree or two. 400psi would be about 47C condensing.
Dual stage? As in two compressors? I assume they're two 7kw units. If so, again you're not a million miles away assuming that that figure includes the fan motor and the fact you're running up towards 50C.
Are you running a seperate coil for each compressor?
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2 Attachment(s)
Re: My first self made EVAP
It is a ZPS two stage copeland,
Attachment 8195
Attachment 8196
On full output it should pull 9.4A at 10C evaporating and 40 condensing and I will check what pressures we are running today, but last i checked, I was drawing more power than that and i hadn't reached a 40C tank temp yet.
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Re: My first self made EVAP
Are you sure its evaporating at 10C. That would be high for this time of year. 0C would be more likely. According to the weather service its 11C in Toronto today, so no way its evaporating a 10C. 3C maybe.
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Re: My first self made EVAP
I stand corrected, I meant that ambient was 10C. I haven't been down to the job today as they are finishing the wood stairs and I can't get in the basement. I will see tomorrow.
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Re: My first self made EVAP
OK, the R410A HP seemed to be running well enough while the weather was a bit warmer. What bugged me most was the high current draw 15.5A when the data sheet says it should be 10.5A.
I put on the gauges and I get suction 4.72Bar, -10C,
discharge is 28 Bar, 48.3C
Liquid from the buffer is 49C and out is 53C
air on 9C and off is about 5C (comp stopped as it was going down and I was about to take pipe measurements on the evap) and the sun went down anyway.
I was going over in the morning and when I got there the EVAP was a solid block of ice.
I think it is overcharged but I have a feeling there is something else as well (perhaps condenser is too small). Any thoughts?
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Re: My first self made EVAP
Quote:
Originally Posted by
MikeHolm
OK, the R410A HP seemed to be running well enough while the weather was a bit warmer. What bugged me most was the high current draw 15.5A when the data sheet says it should be 10.5A.
I put on the gauges and I get suction 4.72Bar, -10C,
discharge is 28 Bar, 48.3C
Liquid from the buffer is 49C and out is 53C
air on 9C and off is about 5C (comp stopped as it was going down and I was about to take pipe measurements on the evap) and the sun went down anyway.
I was going over in the morning and when I got there the EVAP was a solid block of ice.
I think it is overcharged but I have a feeling there is something else as well (perhaps condenser is too small). Any thoughts?
I'd definitely expect that kind of ampage draw on that size compressor with that much differential between low and high side. Try to keep the outlet temp down to 45C if possible. Running at high temps in heating mode will write off your compressor in a short space of time.
Could well be overcharged as your condensing temp and water outlet temp should be within 1C of one another and right now they're 4-5C apart. Your subcooling should be close to your return temp too.
Whats controling defrost and what type of defrost is it?
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Re: My first self made EVAP
That's the problem, it is a York board with defrost built in. The manual gives no indication except that there are jumpers across pins depending on the size of unit. I assume that is for defrost time. There is a bonnet sensor, defrost sensor as well an ambient sensor.
I assume it just triggers the reversing valve.
It also mentions something called "Hot heat pump" but does not define what that means.
Bugger....
The above temp is the highest the unit gets to as my tank setpoint is 49C
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Re: My first self made EVAP
I would say cond side is very good, suction does seem very low for that ambient and condensing pressure.
(when dealing with temps and pressure which are very close, you may just find it is the accuracy of the instruments that you are using.)
The amps are spot on, for those conditions.
You need to work out why your suction is so low, at 9C and high SCT you should be well above freezing.
Do you have sight glass in the liquid line?
what is suction return temperature at the comp inlet.
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Re: My first self made EVAP
Suction return about 6" from the inlet was -10C.
I am thinking of putting in a bigger pump to get a bit more out of the condenser. What do you think?
As BF says try to narrow the gap some....I thought the condenser was a bit small
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Re: My first self made EVAP
Unfortunately there is no sight glass, my next concoction will have one
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Re: My first self made EVAP
Your SCT is 48.3C and water onto the cond is 49C, can not any better than that! (well that is actually impossible)
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Re: My first self made EVAP
I would say that you either a coil design problem or not enough airflow (my guess)
What is your air onto the coil temp, not ambient
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Re: My first self made EVAP
Tomorrow I will put the digi-cools on and take a pic under the conditions. It is supposed to be 10C out tomorrow. I cannot decide if I need more gas or a bit less.
I still don't like the elevated current draw. Not that efficient really...
The defrost is really worrying me but it must just be an electrical setting.
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Re: My first self made EVAP
They are about equal, within .5 deg
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Re: My first self made EVAP
Quote:
Originally Posted by
mad fridgie
Your SCT is 48.3C and water onto the cond is 49C, can not any better than that! (well that is actually impossible)
He's condensing at 48.3C which should be equal to outlet temp. Subcooled temp would be lower. Closer to return temp. At the moment his condensing temp is equal to his return temp, which is too low.
Check your super heat. Should be floating around 3-4K.
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Re: My first self made EVAP
The outlet temp can be higher than SCT, I would say there is a slight error in the readings.
But there is nothing wrong with side.
The low SST is the issue.
With -10C suction temp. nothing wrong with charge.
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Re: My first self made EVAP
I can't get the bloody thing to defrost and I can't get to the entire coil to do it with hot water (design improvement #1 coming up). Luckly it will be 14C tomorrow. I can't ever remember having these temps at this time of the year.
New reading shortly
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3 Attachment(s)
Re: My first self made EVAP
Here are a couple of pics that should tell a tale. EVAP Air on is 11.7C air off is 5.7. SH stayed steady around 7-8C, SC started off around -6-7C and by the end was around -17. The biggest issue is the Dt measured right at the discharge and 6cm from the suction, 55C by the time it reached limit. My 450L tank was to be heated from 20 to 39C. It took 50min...too long.
Attachment 8335Attachment 8336Attachment 8337
I was keeping a 2-3C differential on the liquid side of the condenser.
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Re: My first self made EVAP
I was looking at the high subcooling, reasonable superheat and thought i might have a bit of a high charge (I thought there might be some backup into the condenser) but not too high. So I took a bit out, and i didn't have a scale but it was a couple of seconds on vapour side. Now my SC goes as high as 30 deg and SH is down to around 4 deg. The rest of the above conditions are roughly the same.
Could I be looking at a liquid line restriction?
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Re: My first self made EVAP
Mike not enough info.
Forget what you are using for just for a moment
So what info do we need
Water entering the condenser
Water leaving the condenser
Flow rate if possible
Air temp entering the evap (not ambient)
Air temp leaving the evap.
saturated suction temperature ( SST) pressure/temp relationship
refrigerant temp leaving the evap
refrig temp entering the compressor
Saturated discharge temperature (SCT) pressure/temp relationship (at the comp)
Discharge Temperature (just after the comp outlet)
Liquid temp leaving the condenser
Liquid entering the TEV
Liquid Pressure ( at the TEV inlet if possible)
Current draw of the compressor
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Re: My first self made EVAP
This seems to be beyond me as i need to actually SEE this working to do any figuring. However if i may put my 2 cents worth in, could your evaporator have too closely spaced fins for those temperatures? Maybe the depth of your evaporator is allowing too much T.D. As we all know, once ice forms, it continues to grow and insulates evaporators, reducing performance and reducing air velocity.
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Re: My first self made EVAP
Quote:
Originally Posted by
mad fridgie
Mike not enough info.
Forget what you are using for just for a moment
So what info do we need
Water entering the condenser
Water leaving the condenser
Flow rate if possible
Air temp entering the evap (not ambient)
Air temp leaving the evap.
saturated suction temperature ( SST) pressure/temp relationship
refrigerant temp leaving the evap
refrig temp entering the compressor
Saturated discharge temperature (SCT) pressure/temp relationship (at the comp)
Discharge Temperature (just after the comp outlet)
Liquid temp leaving the condenser
Liquid entering the TEV
Liquid Pressure ( at the TEV inlet if possible)
Current draw of the compressor
Mad, I can get all that again with exception of the pressure at the EVAP( the pressure tap is within 1.5m of the tev). Excuse my ignorance but I assume SST or SCT includes the SH or SC. They should just record the suction temp and discharge temp separately.
My biggest fear is causing damage to the comp in the short term with such a high pressure differential (20bar).
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Re: My first self made EVAP
Quote:
Originally Posted by
mikeref
This seems to be beyond me as i need to actually SEE this working to do any figuring. However if i may put my 2 cents worth in, could your evaporator have too closely spaced fins for those temperatures? Maybe the depth of your evaporator is allowing too much T.D. As we all know, once ice forms, it continues to grow and insulates evaporators, reducing performance and reducing air velocity.
Mike, the coil designer has a lot of experience with heat pumps and long before I came to him for this coil, we talked a bit about how he designs his coils. He would rather have a larger spacing than have a tight package. There is a problem with defrost on this unit but I think it is electrical in nature. The coil is a 5 row and I will post a pic of the tube arrangement when I can find it.
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Re: My first self made EVAP
"SST and SCT" are in other words "Te & Tc", or the gauge pressure converted into a temperature. They are not subcooling or superheat
Example R410a 20Barg = 35C, if this was the discharge pressure then SCT would be 35C, not to be confused with discharge temperature, or liquid pressure or liquid temperature.
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Re: My first self made EVAP
What size tube are using in the evap coil and how many circuits are there?
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1 Attachment(s)
Re: My first self made EVAP
Hi Mad,
Here is a pic of a similar coil. The liquid line should be in front of the discharge line facing in the same direction (up). All tubing is 0.5" od and there are 4 circuits coming to a common 1.375" manifold which you can see in the pic. The overall coil size is 30" by 48" long. The tube rows are 1" apart and the U bends are 1.25' on centre.
According the the pic I posted above, what the digi-cools show is the SST (0C) and SCT (46C). I'm still getting used to everything.
Attachment 8340
Disregard the ends that you can see at the corners. It is not quite the same coil
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Re: My first self made EVAP
Well, my issues with defrost were all down to an improperly grounded RV wire from the defrost control. whenever the control wanted to go into defrost, that wire went to ground and the valve didn't move. All seems well now.
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Re: My first self made EVAP
Thats a weight off your mind. Not sorry to put that to bed I'm sure
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Re: My first self made EVAP
Yes, well...on to the next thing which is programming a control that will do everything needed in one product. I am being pushed by Jens (the old Dane HP builder) to use the TAC Xenta controller and control all pumps, mixing valves and fans. I don't know if there is a difference between this type of controller and and equivalent PLC from Siemens or Allen Bradley. Any idea? As we have seen with most of the package North American stuff, it still uses 30 year old control technology and it can be improved on.
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Re: My first self made EVAP
Whats wrong with the Lodam? Have you hooked it up to your own unit yet?
Better interface and more complete solution for your purpose than the other products I think