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Thread: Hot Gas Defrost
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17-08-2005, 11:50 PM #1
Hot Gas Defrost
Installing a new system, just realised evaporator does not have electric heaters. its a 20 Kw evap
So , Im going to have to go hot gas defrost
The check valve.........does it go after the expansion valve
Its better I look like an idiot asking, but I want to get it right
Thx
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17-08-2005, 11:59 PM #2
Re: Hot Gas Defrost
The chek valve should be installed parallel to TEV. The chek valve direction-to liquid line.
Vaidas
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18-08-2005, 12:14 AM #3
Re: Hot Gas Defrost
Ignore that I wrote above if your system has one compressor and evaporator. In that case you don't need the chek valve, if the liquid line has a solenoid of course.
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18-08-2005, 12:32 AM #4
Re: Hot Gas Defrost
If your system is a single evporator and unit, then you will not be able to use a two pipe hot or sat gas defrost method and will have to use a three pipe system. Take a 1/2 or 5/8 tee off the discharge and pipe (or top of reciever, if it contains enough volume of sat gas vapour to effect defrost) to a tee between the expansion device outlet and the distributor with a solenoid valve for control. The suction gas pressure to the compressor should be controlled with a crankcase pressure regulator. In practice it is a pretty crap way (Comp nearly always runs 100% of the time and eventually fails) of effecting a defrost and you would be far better to fit defrost heaters.
it's only a fridge, fix it. ;)
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18-08-2005, 02:59 AM #5
Re: Hot Gas Defrost
Take a look here http://www.sporlan.com/5-158.pdf:)
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18-08-2005, 09:09 PM #6
Re: Hot Gas Defrost
Hi Wambat.
The link doesn't work for me
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18-08-2005, 09:33 PM #7
Re: Hot Gas Defrost
I think that the link should be without the
like this i think it will work http://www.sporlan.com/5-158.pdf , nothing should be after the final extension of a file , that's what's i've mentioned from my experience in computersEngineering, sciences, math, physics and my brain will generate "not responding " soon
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18-08-2005, 10:07 PM #8
Re: Hot Gas Defrost
Hello Aiyub
The post the guys put up for you from Sporlan is NOT for defrost purposes this is for low load conditions/capacity control on a/c systems you would need more controls i.e. suction accumulator/pan loop/ solenoids/etc for defrost use
regards
Dave G
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19-08-2005, 02:04 AM #9
Re: Hot Gas Defrost
Dave is correct, I believe this is better http://www.bmil.com/ballyrefrig/thermosaver.htm
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19-08-2005, 06:32 AM #10
Re: Hot Gas Defrost
Hi mate,
Is this a freezer application?
My opinion, I should install heaters, vene if you have to remove the evaporator once again.
Like the posters said, if it's a 1 evap/1 cond situation, you will also need to to install a TEV on your condensor and 2 check valves. A lot of work and the material will cost more than the heaters.
In case of a reversal cycle, you will also need a large enough liquid separator.
Otherwise your compressor will pump liquid after a defrost.It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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19-08-2005, 10:17 PM #11
Re: Hot Gas Defrost
Originally Posted by Peter_1
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20-08-2005, 10:16 PM #12
Re: Hot Gas Defrost
Originally Posted by Peter_1
Yes, it is a freezer room.
Ive decided to install heaters, instead of going the hot gas defrost route
I ordered 8 straight heater coils, cost £20.00 each. Total cost £160.00
Fitted them today, now I dont have to worry about check valves and compressor burning out, etc
Thanks for everyones help........I appreciate it.
Abe
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21-08-2005, 12:17 PM #13
Re: Hot Gas Defrost
Originally Posted by vaidas_78It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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22-08-2005, 12:34 AM #14
Re: Hot Gas Defrost
Originally Posted by Peter_1
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22-08-2005, 09:10 AM #15
Re: Hot Gas Defrost
You're right, this wasn't a good example.
This is a better one http://www.books4hvac.com/rb/Heat_Pumps1.htm
I hadn't look very weel when I posted this link.
They use a 3 way valve instead of a 4 way
BTW, what do you guys think of the Thermosaver system?
Two liquid separators, one with a succool coil in it.
Why 2?
Is the subcool coil in defrost mode acting as a small condensor?
Where is the heat coming from to defrost the coil? Only from the absorbed power of the compressor?
Where happens the expansion?
What about excessive compressor SH?
For smaller applications like small ice machines and small evaporators this will work fine but for the system like Aiyub, I doubt.
Any comments on this?Last edited by Peter_1; 22-08-2005 at 10:15 AM.
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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23-08-2005, 01:00 AM #16
Re: Hot Gas Defrost
Hi Peter, it looks to me you have been confused.Thermosaver is not a heatpump and it use a 3way valve for defrosting, not for a cycle reversing.In this system the hot gas and a liquid are sharing the same pipe,so it needs 3way valve and two chek valves.
The subcool coil in the defrost mode forces the liquid to boil in accumulator.
The crankcase pressure regulator(pos.H) protects compressor from overloading during the defrost cycle and also evaporizes some liquid.
Where is the heat coming from to defrost the coil?
Regards Vaidas
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23-08-2005, 08:00 AM #17
Re: Hot Gas Defrost
Originally Posted by vaidas_78
Valve H act while defrosting as an AEV.
The vaporized refrigerant picks up some heat passing through the suction line. As it passes through the compressor, the heat of compression raises the temperature to such a level that it continues to heat the evaporator and remove the frost.
Further more, the liquid coming from the evaporator encounters a serious temperature drop when entering the right accumulator (with the subcool coil)
So the hot discharge gasses going to the evaporator for defrosting will undergo a serious cooling, so the net availbale heating effect will seriously decrease.It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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24-08-2005, 12:11 AM #18
Re: Hot Gas Defrost
Hi Peter,
The main parameter for the discharge temperature(and also pressure) increasing is a compression ratio. Higher compression ratio - higher the temperature at the end of the compression.Low temperature compressors have the high compression ratio.What's why they cannot be used in high temperature aplications as a high suction pressure would increase the discharge temperature and pressure greatly.For this reason thermosaver is using the crankcase pressure regulator. During a defrost cycle DP is not very high but it's normal .Of course the suction gas temperature affects the discharge temperature but just slightly.
What I don't like in this system is that the hot gas shares the same pipe with the liquid.At the beginnig of the defrost the hot gas will push the liquid all along the line and evaporator to the suction line.What's why they are using two liquid separators,I thik. What would happen if the liquid line would be very long?
I would rather choose a three pipe system whith the one accumulator.
What do you think?
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