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Re: Buffer Tank Assisted Defrost
What we really need to know is the saturated temps (pressure converted into temp),
It is the differences between the saturated temps and the real temps that determine some of limits.
Without the sat temps, actual temps have little meaning, for the refrigeration system.
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Re: Buffer Tank Assisted Defrost
Attachment 8382
This how you do it if want to shorten defrost time, and have energy benefits from the defrost.
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Re: Buffer Tank Assisted Defrost
I better explain.
the tank is heated ( in heating mode), by the liquid refrigerant leaving your indoor coil, so there is no loss of energy from your home. This will also benefit the outdoor energy absorption (better cooling), as we have sub cooled the liquid, reducing the vapor fraction leaving the TEV, in cold conditions the outdoor coil refrig pressure drop will reduce and increasing the LMTD (temp across the coil will be more even) better distribution is likely to occur and more than likely lifting the comp suction pressure (exact performance is equipment specific)
We now have an energy source, that has no negative effects on your internal heating. (even some positives),no losses of heat or any extra energy introduced.
We go into defrost, ( I would turn the fan off only to reduce the wind chill factor because no heat is being produced) The boilng refrigerant, passes through the warm tank, absorbing lots of energy (cooling the tank down), because we are absorbing this energy defrost will be quicker. Compression ratios will be smaller, so more efficient. But the biggy is that we are not removing any energy from the home at all due to the defrost.
Because the tank is warmed (close to saturation temperatures, not compressor discharge temp), you are not going to get very excessive suction superheat temps (as you would with your original drawing).
On completion of defrost leave fan off until the indoor coil reaches 40C + (ramp slowly)
So all issues are resolved, and large energy savings to boot.
You can post on HVAC TALK along withe drawing.
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Re: Buffer Tank Assisted Defrost
Thanks mad fridgie,
I am now really confused and frustrated.
The only difference between your proposal and my original proposal back in post #1 is
that you are bypassing the indoor coil in defrost mode. (and bypassing the tank in cooling
mode but that was not being discussed)
When I made my original proposals the following replies were given:-
big Freeze---
"Not really feasible as yours is an air to air unit and therefore the unit is designed
to heat air and not water."
Nevgee---
"Have you considered the amount of superheat and what effect that would have on the
compressor?"
you
"In simple terms, the vapour will be very highly superheated, which in turn cause very
high discharge temps (damage to compressor)"
So to summarize, my original proposal in post #1 would work.
pilko
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Re: Buffer Tank Assisted Defrost
The devil is in the detail. And is not the same
Me was referring to post 67
lets put it this way.
1000KVa, what size cable at?
a; 1000v
b; 10V
are they the same?
If it was sized for 1000V, what would happen if you then used 10V
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Re: Buffer Tank Assisted Defrost
"the tank is heated ( in heating mode), by the liquid refrigerant leaving your indoor coil"
Same with mine.
"We go into defrost, ( I would turn the fan off only to reduce the wind chill factor because no heat is being produced) The boilng refrigerant, passes through the warm tank, absorbing lots of energy (cooling the tank down), because we are absorbing this energy defrost will be quicker. Compression ratios will be smaller, so more efficient. But the biggy is that we are not removing any energy from the home at all due to the defrost.
Because the tank is warmed (close to saturation temperatures, not compressor discharge temp), you are not going to get very excessive suction superheat temps (as you would with your original drawing)"
same with mine.
Why will my system not work
pilko
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Re: Buffer Tank Assisted Defrost
NO it is not.
I am going to put 100amps at 10V, down a 0.5mm wire, or 1 amp at 1000V down the same wire, same result!
Is there going to be "any" difference between the 2
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Re: Buffer Tank Assisted Defrost
I Think I understand you now.
Are you saying that the tank requires two coils of different specs. because the flow through them
is different in heating mode and defrost mode?
pilko
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Re: Buffer Tank Assisted Defrost
Yes i am talking about pressure drops, because at each stage you are different states and densities.
Look at your evap inlet (cooling, defrost mode) small pipes, designed for primarily for liquid flow (high voltage), if you use your system vapour will pass through (low voltage), massive pressure drop, causing high superheat (not high temp) and very low comp inlet pressure. You could use one coil in the tank, but valving would be bigger more expensive and also has other issues.
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Re: Buffer Tank Assisted Defrost
Thanks mad fridgie,
Based on hopefully increased knowledge, would this work as it would be simple for me to build:-
Heating mode.
B closed A open till water in tank reaches X*C.
Then A closed B open.
Defrost mode.
B closed A open.
Cooling mode.
A closed B open
pilko
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Re: Buffer Tank Assisted Defrost
Yes it would work, but is not energy efficient! You are stealing energy from the house, worse than turning the fan off.
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Re: Buffer Tank Assisted Defrost
In both your case and my case the heat is being generated by the heat pump.
My tank would heat much faster as it is heated by hot vapour."Short time not heating the house"
your tank heats much slower as it is heated by the cooler fluid. "heating tha house at a lower temperature"
pilko
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Re: Buffer Tank Assisted Defrost
No it is not,
in your case the heat is produced by the compressor and is useful to your house heating , in my case the heat made by the outside ambient.
(I use heat because you do, I prefer the word "energy") This is not an element! You can not think of it as an element. This your mistake!
The energy in mine has no use in the house.
Speed is not important. As long as the energy introduced into my tank is equal to what is required for a fast defrost.
On this side of the equation, what i am doing does NOT effect the energy rejected into the home!
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Re: Buffer Tank Assisted Defrost
In simple terms (and wrong terminology)
You have 20Kw energy leaving your compressor, 10Kw is taken by the house, normally the remaining 10kw is pushed back outside, where energy renters the refrigerant 7kw, the comp compresses 3Kw, back to 20Kw.
So there was 10kw of energy that goes round and round, in my system I steal some of this say 1Kw, this is replaced for outside, so the 7Kw goes to 8Kw.
Yours steals the 1kw from the house heating you now have 9kw for house heating. the outlet of the indoor coil does not change. so the 10Kw still just flows round and round.
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Re: Buffer Tank Assisted Defrost
In both cases the energy is produced by the uotside ambient heating the outdoor coil and then compression.
In your case, some of that energy is transferred to the tank before the energy transfer medium is returned to the outdoor coil.
In my case all of the energy is transferred to the tank for a shorter time then it is all transferred to the indoor coil before the energy transfer medium is returned to the outdoor coil.
I do not see the net difference.
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Re: Buffer Tank Assisted Defrost
Good explanation Mad, 1 pint for you.
The big question for Pilko is to figure out how to make a tank with two HX that works for him.
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Re: Buffer Tank Assisted Defrost
Thermia have a system not to far off this for defrosting the outdoor unit of an Air/Water heat pump. It utilises some of the stored energy as the heat source (indirect) to remove the ice in reverse cycle.
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Re: Buffer Tank Assisted Defrost
I should also point out that Danfoss now own thermia!
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Re: Buffer Tank Assisted Defrost
@ Richard --- thanks for the info.
@ Mad --- Thank you for all of your support and a special thanks for being so patient with me.
Most people would have given up on me by now.
It is obvious that I need to study the thermodynamics of the refrigeration process.
Regards
pilko
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Re: Buffer Tank Assisted Defrost
Quote:
Originally Posted by
750 Valve
This is quite a funny read, I have long subscribed to the theory that the North America is about 10 years behind the rest of the world when it comes to refrig and air and this proves it!
I can't believe it's that hard a concept to grasp! The rest of the world caught on and designed R/C systems the same way for the last 15 to 20 years but no, good old US of A reckons it can't be done!
Whoa Cowboy, the gent pilko is north of the border not one of ours!!!
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Re: Buffer Tank Assisted Defrost
I would advice that you install a accumulator, turn your fan off.
I only showed how it could be done using a buffer, that it had benefits and to help you to understand why/what you had drawn was wrong.
If you want to understand refrigeration, you must first understand that the system is a loop and not a number of components joined together.
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Re: Buffer Tank Assisted Defrost
Quote:
Originally Posted by
Emmett
Whoa Cowboy, the gent pilko is north of the border not one of ours!!!
Ha ha Emmett, tis true, but he is using a Carrier system......not Canuk built, last time I checked
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Re: Buffer Tank Assisted Defrost
Hi Mike, have a look on HVAC TALK, for me please "I have been banned."
any comments from them
search barbar.
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Re: Buffer Tank Assisted Defrost
Will do, I haven't been able to register on it as it keeps kicking me out. I will try to re-register tonioght.
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Re: Buffer Tank Assisted Defrost
You are a bad boy as well. Get to the back of the room with me.
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Re: Buffer Tank Assisted Defrost
I never learned anything in school because i kept passing girly pictures to you at the back of the class. Now look where we are...
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Re: Buffer Tank Assisted Defrost
Quote:
Originally Posted by
MikeHolm
Ha ha Emmett, tis true, but he is using a Carrier system......not Canuk built, last time I checked
True however the comment was in reference to Mr pilko not his equipment and I suspect that if it is a carrier unit it was engineered in asia or europe and built in mexico anyway so the the equipment is likely American in name only. It is just about impossible for a manufacturer to manufacturer in America these days. Any way you too shall have a pint for the great assistance and patience you have shown our new friend Pilko.
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Re: Buffer Tank Assisted Defrost
And a pint to you as well, tis the season as you know.
I believe his is a standard split and it is many years old so i suspect it was made in the US of A. I will check it out at Xmas and bring him a pint (I'll be in the neighbourhood).
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Re: Buffer Tank Assisted Defrost
@ mad fridgie,
Just took a look into my heat pump, It does have an accumulator. Is it OK to go ahead and run defrost with indoor fan stoopped? If yes:-
1 What precautions should I take?
2 What if anything can I monitor to reduce risk of damage?
regards
pilko
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Re: Buffer Tank Assisted Defrost
Quote:
Originally Posted by
pilko
@ mad fridgie,
Just took a look into my heat pump, It does have an accumulator. Is it OK to go ahead and run defrost with indoor fan stoopped? If yes:-
1 What precautions should I take?
2 What if anything can I monitor to reduce risk of damage?
regards
pilko
OK, firstly lets look at control, and also taking note of the "Pros" concerns. (remember I do NOT know your particular equipment)
Because of how you measuring ice, you could but a defrost fail safe in (If after "x" mins the coil is not defrost slowing bring fan on. (you will still have a cold draft when the fan is on, but is a "just in case")
That covers all issues about the ability to defrost.
As far as protection, firstly look at the size of your accumulator (volume), is the volume greater than the total volume of liquid refrigerant in your system. ( again not quite a true fact but thing of the volume of refrigerant as water "2kg of refrigerant = 2 litres") The weight of refrigerant should be indicated on the outside unit. If the accumulator volume is over or close to the refrigerant volume, then no worries.
If it is greatly smaller, then install a larger one.
We could look at electrical protection, but would be expensive and very complicated software.
pressure transducers, temp sensors, comp current sensor, with pressure/temp comparability.
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Re: Buffer Tank Assisted Defrost
Thanks mad fridgie,
There will be some frost tomorrow morning, so will check the accumulator and if OK, will do some testing then.
pilko
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Re: Buffer Tank Assisted Defrost
Pilko, did you get the weather bomb yesterday?
Your defrost control is probably on one board with the pressure switches terminals and RV output etc. I don't know what board in on your unit but on the one I have been working on, the fan stops during defrost. If it doesn't stop, I have a simple defrost control which will trigger the RV and stop the fan.
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Re: Buffer Tank Assisted Defrost
Hi Mike,
The original Carrier board inside the heat pump operates the RV, stops the outdoor fan, and controls the time between defrosts (No demand defrost). The indoor fan is controlled by the room thermostat.
I control frost-level defrost, and temperature controlled indoor fan with a home made board in my "cave"
My board logs coil inlet and outlet temperatures, outdoor temperature, frost level on outdoor coil, fan CFM and Heat pump power.
Protections are still operational on the outdoor board.
pilko
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Re: Buffer Tank Assisted Defrost
No weather bomb and none forcast.
BTW How do I edit a post?
pilko
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Re: Buffer Tank Assisted Defrost
@ mad fridgie
"As far as protection, firstly look at the size of your accumulator (volume), is the volume greater than the total volume of liquid refrigerant in your system. ( again not quite a true fact but thing of the volume of refrigerant as water "2kg of refrigerant = 2 litres") The weight of refrigerant should be indicated on the outside unit. If the accumulator volume is over or close to the refrigerant volume, then no worries.
If it is greatly smaller, then install a larger one."
Nameplate charge = 4.94 Kg
Volume of accumulator = 3.6 L
Using density at 21*C = 1490 Kg per cubic metre
Capacity of accumulator = 3.6 X 1.49
Capacity of accumulator = 5.4 Kg
Should I go ahead ?
pilko
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Re: Buffer Tank Assisted Defrost
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Re: Buffer Tank Assisted Defrost
Thanks mad,
Forecast a bit of frost overnight. Will give it a try in the morning.
pilko
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Re: Buffer Tank Assisted Defrost
@ mad fridgie,
Did a defrost without indoor fan this morning ----SUCCESS !!!!!
Outdoor temp was -4*C
Restarted fan when indoor coil reached 40*C.
pilko
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Re: Buffer Tank Assisted Defrost
How did it feel in your house?
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Re: Buffer Tank Assisted Defrost
@ mad fridgie,
"How did it feel in your house?"
Very comfortable.
BTW defrost did not take any longer than with fan running.
I will check after several defrosts that deep frost (ice that forms deep in the coil due to incomplete defrost) does not start to build up on the outdoor coil.
pilko