Buffer Tank Assisted Defrost

[pilko]

Hi everyone,
I am new to this forum and as I was just lurking,I discovered buffer tanks.
I run a 2 1/2 ton air to air unit.
I would like to use a buffer tank to assist the defrost process and eliminate the
cold air into my living area by stopping the indoor fan during defrost.
If this mod.is feasable would the buffer tank/heat exchanger be installed in the
position shown in the upper diagram or lower diagram?

Regards,

pilko.

[Bigfreeze]

Not really feasible as yours is an air to air unit and therefore the unit is designed to heat air and not water.
In diagram one, when heating, the majority of heat will be lost to the buffer until the buffer reaches temp which means cooler air at your duct for a long period of time and my guess is it could become very problematic when the system defrosts as the hot water will raise the temp of the suction gas to such a level that the cooling that the gas provides to the compressor would be virtually nil, so your compressor life would be shortened.

In diagram 2, it adds no benefit to the system at all as in heating it will act as it does now except it will also have 200L of water to heat and in defrost you will still get cold air at your duct, although your defrost may be a little quick due to the extra energy provided by the tank.

If it was me I'd leave well enough alone. They're not very compatible in this application.

[pilko]

Thanks Bigfreeze,
My way of thinking (although it may be flawed) is as follows:-
In scenario #2 in heating mode the vapour will be cooled as it heats the buffer water on is way to the compressor.
In defrost mode, the vapour heats up as it passes through the buffer on its way to the indoor coil. The indoor fan would not be running so the heated vapour will continue out to be compressed and then heat the frosted outdoor coil.

regards

pilko

[nevgee]

Have you considered the amount of superheat and what effect that would have on the compressor?

[mad fridgie]

The fan should stop on defrost any way, and not restart until the coil has warmed back up.

[pilko]

@ vevgee
"Have you considered the amount of superheat and what effect that would have on the compressor?"
I would ensure that the amount of heat recouped is no greater than that in a normal defrost.

@ mad fridgie
"The fan should stop on defrost any way, and not restart until the coil has warmed back up."
The indoor fan does not stop during a normal defrost as it is required, to pull heat from inside the home in order to heat up the cold vapour and hence the outdoor coil.

The heat I am suggesting using from the buffer tank would be used instead of that heat which is pulled from the house which causes cold draught and room cooling.

[mad fridgie]

You have enough thermal mass, natural convection and heat of compression to defrost the outdoor coild without the fan running.

[pilko]

@ mad fridgie
"You have enough thermal mass, natural convection and heat of compression to defrost the outdoor coild without the fan running."
The only thermal mass that I have (without the buffer) is in the 20 feet or so of liquid line.

regards

pilko

[mad fridgie]

What about the mass of the coil, the hot refrigerant within the coil and the mass of the housing
This nothing new, this how it is done in most parts of the world, I have had these in my home for 20 years, no problems. Just try it!

[pilko]

Thanks so much mad fridgie.
I am certainly going to try it as soon as the OD temp dips again. We are having a heat wave right now (+6C)
This has blown me away, every one I know has their indoor fan running during defrost.
I will report back as soon as I have tried it.

regards

pilko

[MikeHolm]

Pilko, where are you?

[pilko]

Hi Mike,
I live in New Germany, Nova Scotia. My son lives in Toronto so I go there quite often.

pilko

[MikeHolm]

Cool, I'll be in Mahone Bay for Xmas

[pilko]

Great,--- Mahone Bay is a beautifull spot.
I just checked your site. I see you're an Electronics Tech. Electronics is my background too.
My Heat Pump is my hobby and I have made several mods to the control circuitry. I also measure and track the parameters on my computer and display them on my TV ( the missis thinks I'm crazy)

pilko

[MikeHolm]

My electronics was farther in the past than I want to admit and for some reason I am much better with relays and old style controls than figuring out pre-programmed controllers. I've been doing way more boilers and solar than pure electronics anyway. BTW, my misses KNOWS I'm crazy

[tectron]

low pressure problem in defrost mode on air water heat pump with EEV
ideas?

[Bigfreeze]

low pressure problem in defrost mode on air water heat pump with EEV
ideas?

Lack of water flow.
Water drops in temp, which causes gas temp and pressure to drop. Its possible the safety for the HX is controlled by low pressure rather than a min flow temp, hence the LP fault.

[pilko]

@ mad fridgie
I did some more research and testing re. your recommendation to stop the internal fan during defrost.I realize that is what you are doing but I am nervous.
Firstly my supplier says he doesn't recommend it. Then I found the attached comment on the HVAC Talk forum.
Because of my nervousness I did two defrost tests,one at 960 CFM and the other with a lower fan speed producing 530 CFM (the graphs are attached).
I would greatly appreciate your comments --- or anyone elses for that matter.

Regards

pilko

[mad fridgie]

Just a question first, you do turn off the outdoor fan during defrost!

[pilko]

"Just a question first, you do turn off the outdoor fan during defrost! "

Yes

[mad fridgie]

It would seem that in your neck of the woods, that old principles rule.
With the fan off will the indoor coil become very cold, "yes" who cares!, your discharge pressures will be very low, so compression ratios will be low so no issues.
Do your system have an accumulator.
Your outdoor coil 'in defrost' should be temp terminated, not just time.
You indoor fan should restart on temp (when the coil gets above 40C, to stop cold draft start).

[pilko]

@mad fridgie,
I really appreciate your help and patience.
I have just received another conflicting answer in the last few minutes from the HVAC Talk forum.

regards

pilko

[pilko]

Hard to read ---attaching link

http://hvac-talk.com/vbb/showthread.php?t=978262

[mad fridgie]

Of course a big heater would cure the cold draft problem. No arguments.

It is clear that your type of system is common in North America, I suspect they are just AC units, with a reversing valve installed, basic controls and not real thought but into the heating side.

This issue has been resolved for at least 20 years, check out all your well known Japaneses brands.

[MikeHolm]

There are a lot of Chinese brands starting to be installed around, Haier and the like. A 4kw HP is going in for about $1800-2000 CDN from what I hear. I suspect there is not much knowledge on service by the installers, knowing most of our trades.

Most of the Japanese ones are Fujitsu and Mits. Daiken has only just started selling in North America.

[pilko]

@ mad fridgie,
Are you by any chance refering to the split type with a wall unit whereas the others and myself are refering to the split, ducted air system.--- I just wondered if that would explain the differences in opinion.

pilko

[MikeHolm]

The rest of the world, to my knowledge, does not heat homes the way we do, forced air, A coils etc. so all the stories i hear are using the split wall hung systems, fujitsu, mitsubishi etc.

Sorry to answer for you Mad. Deny me beer if I am wrong.LOL

[mad fridgie]

"No" a fully "16Kw nominal" ducted system (heating 220M2) 7 rooms (11 outlets) with hall acting as a mixing chamber (so indirectly heated by all the return air) outdoor bit is outdoors, indoor bit is in the roof cavity. 12 meters pipe between. This one is toshiba, the last one had 2 outdoor units to one indoor unit (daikin). Similar set up (more rooms) We get down to -6C outside, design is based upon 2C averaged.
Regardless if ducted or high wall the same problems occur. The refrigerant does not know if it is in a duct or on the wall.

[pilko]

Hi mad fridgie I do not doubt what you are doing at all, I am envious but nervous.
Please check the link in post #23, there have been some additional comments on the other site.
Would it be possible for you to post your comments on that site as they are adamant about not stopping the fan.
It is hard to make a decision when experts have opposing opinions.

regards

pilko

[mad fridgie]

I do not, have any aux heaters in my duct!
Your ducting, are the outlets at high level or low level?

[mad fridgie]

Tried getting onto the other site, can not remember password.

[pilko]

@ mad fridgie,
My ducting, indoor fan and "A" coil are all in my basement. My outlets/registers are on the main floor (bungalow)
Did you read the comments on the other site?

pilko

[pilko]

This shows performance for last 2 hours.
Defrosting seperation 72 minutes.

Green = Discharge air temp
Dark blue = Return air temp
Green = Outdoor temp
Light blue = Frost level on outdoor coil

pilko

[mad fridgie]

Right time to get technical (copy onto the other site)

Rough examples

In normal heating mode ; (R22 I guess)
1;ambient = -2C
2: return air = 20C
3;Estimated SST -8C
4;Estimated SCT 45C
Basic COP = 2.85 (heat)

When defrost with fan on!
SST 0C
SCT 27C (min limit for comp, but would expect lower in real world)
COP 5.51 (heat) Remember that the energy for defrost comes from inside your house, and has to replaced.The cooling COP is much higher

So what does this mean, you require twice as much energy to replace the heat you loose when on defrost when the fan is running.

Now with out fan running (no cold draft and minimum energy drawn from the house)
SST -20C
SCT 27C
COP 3.39 (heat)

So as you can see, the lower COP in this defrost cycle means less energy is removed form your house.

Also remember that on this nominal 10Kw the comp we still draw 2.3Kw, which is defrost the evap coil (which becomes a condenser during defrost) What does this mean in defrost terms, the comp power draw alone will defrost 54.5lb of water an hour. 1/2 the weight for 1/2hour and so on. You are still getting some energy from the mass of the indoor coil and surroundings.

Defrost will be slower, as the total amount of heat rejected to the defrosting coil will be less when the fan is not running.

Well I hope that makes sense

[mad fridgie]

Yes did read what they said.
The only thing I do not know is how your machines are built or designed, I suspect same design as Noah used on his ark!
You need a control scenario
The fan is OFF during defrost
The fan ONLY comes on when the indoor coil is up above 40C (this reduces the cold draft) However you still have a bit of cold air in the duct, I presume your basement is colder than your living areas!
Defrost is terminated when the outdoor coil is above 4C (then time as back up)

[pilko]

@ mad fridgie,
"Right time to get technical (copy onto the other site) --- do you mean you have copied to the other site or are you asking me to?

pilko

[mad fridgie]

Yes...............................you

[pilko]

---------------Done

[mad fridgie]

Just seen the experts response. What expert!!!!!!!!!!!!!!!!!!!!!! (on another site)

Of course is takes the same amount of energy to defrost 10lb of ice. Who said it did not!

The argument is that there is not enough energy to defrost coil without the fan running.
I proved that there is, that it is more energy efficient and most of all more comfortable.

I get the impression you do not even have temp defrost termination!

[mad fridgie]

Mad Fridgie is barbar

[pilko]

@ mad fridge,
"I get the impression you do not even have temp defrost termination!"
Are you refering yo me or the expert on the other site.(this is all getting very confusing)

pilko

[mad fridgie]

So Pilko, to both really, tried to post of hvac-talk, sort got kicked off,
I question and gave answer to your questions, but they have been deleted.
So I have tried another approach, lets see what happens.
No kicked of that way as well?
So sorry can not help on the other forum.

[pilko]

In an attempt to settle the argument I have recorded a defrost at 1000 CFM and a second defrost at 500 CFM.

Red = Discharge air temp From "A" coil
Dark blue = Return air temp to "A" coil
Green = Outdoor temp
Light blue = Frost level on outdoor coil

[mad fridgie]

Do this by hand
Turn off the fan, at start defrost! Do not turn the indoor fan back on until the coil reaches 40C! (back in heating mode)
Turn defrost off when outdoor coil is free of Ice (not on time)
Oil is not an issue!
The only reliability issue is the chance of liquid flood back, do you have an accumulator ( a big thing before the comp inlet "big pipe") if not then only "maybe" would you need the fan on. (a bit more complicated than I just stated)

[mad fridgie]

You are measuring all the wrong data!
But i am also interested in how you are measuring your ice build up?

[pilko]

Do this by hand
Turn off the fan, at start defrost! Do not turn the indoor fan back on until the coil reaches 40C! (back in heating mode)
Turn defrost off when outdoor coil is free of Ice (not on time)
Oil is not an issue!
The only reliability issue is the chance of liquid flood back, do you have an accumulator ( a big thing before the comp inlet "big pipe") if not then only "maybe" would you need the fan on. (a bit more complicated than I just stated)
The test I just did at 500 CFM was as follows:-
1 As soon a HP went on DF I reduced fan speed to give 50% CFM
2 My defrost ends as soon as the frost is removed (detected by my frost sensor)

pilko

[pilko]

There is no accumulator.

[mad fridgie]

Good about the defrost termination.
Turn of the fan.
Do not measure the coil outlet temp. It will give you false readings. Less airflow lower temps, no air flow very low temps. Less mass so reduced energy removed from your house.
Turn fan back on only when coil is hot.

[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!

[mad fridgie]

Not to good then!
We measure pressures and temp around the comp (as the temps you are reading are the process variables (after the fact) not the system variables (driving force)

[mad fridgie]

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!

Good on your mate!

[pilko]

Not to good then!
We measure pressures and temp around the comp (as the temps you are reading are the process variables (after the fact) not the system variables (driving force)

Are you refering to my lack of an accumulator.
Excuse my ignorance --- I am an electronics man and sadly lacking in Fluid and vapours.

pilko

[MikeHolm]

@ mad fridge,
"I get the impression you do not even have temp defrost termination!"
Are you refering yo me or the expert on the other site.(this is all getting very confusing)

pilko

Guys, maybe i can shine a bit of light on the current north American technology (LOL). Dealing with this york unit, with a johnson controls board, the defrost is 1) based on 6 hrs comp run time, 2) has a liquid line sensor and an ambient sensor. The sensor only allows defrost at temps from -5C to 10C and will de-energise the fan, energise the crankcase heater (if there is one), energise the RV, energise stage two if there is one, start a max 4.5min cycle.

There is a defrost curve for the 4 different HP outputs available by moving a jumper. With this one, the defrost is terminated by both liquid line temp (24C) and/or time.

[MikeHolm]

So Pilko, to both really, tried to post of hvac-talk, sort got kicked off,
I question and gave answer to your questions, but they have been deleted.
So I have tried another approach, lets see what happens.
No kicked of that way as well?
So sorry can not help on the other forum.

Mad, i have also done as you did and got kicked off as well. You have to post in a newbe forum thread for a while until you can prove you are in the trade. I haven't bothered.

[mad fridgie]

You are starting to get, some better answers on HVAC Talk. (not right but moving in the direction)
Defrost on demand, the way to go!
The bit others are mis-understanding is the amount of energy removed from your home during defrost. Which has to be replaced, and the cost of this replacement.
Also understanding of the non steady state nature of refrigeration.
You do need to measure pressures. (this determines comp performance)
The carrier may well not be designed to have the fan off, this could just be mechanics, nothing to do with energy.

[pilko]

The answer lies in these images. The first image shows 2 defrosts, the first at 1000 CFM and the second at 500 CFM. When I zoom and put them together in image two, the area under the 20* return temp (-dT x Time) is only 29% larger with a 500 CFM defrost BUT considering the CFM is only half, the heat loss is only 64%.
It is logical to conclude then that heat loss at 0 CFM will be a small fraction of heat loss at 1000 CFM
I will do the complete calcs using air density and specific heat.
Anyway the chart appears to prove your theory.

pilko

[mad fridgie]

Nice info, with good calculations (on HVAC Talk). It always difficult to know what somebody really knows or not.
You seem to have a good handle on this side.

[pilko]

The Calcs:-

At 1000 CFM Average dT of the air = -9.04
Time = 138 seconds
Heat Loss = CFM/60 x dT x Density of air x Specific heat of air
= 1000/60 x 138 x 9.04 x 0.075 x 0.2375
= 370 BTU
At 500 CFMAverage dT of the air = -10.3
Time = 156 seconds
Heat Loss = CFM/60 x dT x Density of air x Specific heat of air
= 500/60 x 156 x 10.3 x 0.075 x 0.2375
= 238 BTU
It should follow that the heat loss at 0 CFM will be very low

pilko

[mad fridgie]

Just seen the answer HVAC Talk,
with a blocked filter, you get poor refrigeration performance which leads to irregular ice build up ( this comes down to distribution, vapour liquid fraction "x"), and can mislead the defrost sensor.
When ice is heavily formed (due to faults) normal defrost (time limited) will not clear the coil.
You can post this reply!

[mad fridgie]

HVAC Talk
Well the answer you would expect, from someone who does not understand the principles of refrigeration.(cause and effect)
No wonder heat pumps have a bad name when the wrong advice is given.
I will defend though, a standard unit may not have the smarts or the mechanical components to ensure correct operation and reliability to run with out a fan, that does not mean that is correct engineering, or the reason they state are correct, they are not!

[MikeHolm]

Mad, I cannot tell if some of the conversation above is you or "HVAC talk" talking. Uggg

Regardless of the math, any object in still air will react faster to internal heat in still air than in moving ambient air. Pure common sense. Don't you freeze faster when its windy out?

[mad fridgie]

It is me, replying to "hvac talk"
I might know a bit about refrigeration, but I am bloody useless when it comes to computers
I think the OP understands where I coming from??????????????

[pilko]

It is time for me to make a decision.
Mad fridgie You have provided valuable technical information, the other forum has not.The only usefull information the other forum has provided is obvious, that the heat pump will run longer to defrost the coil. My graph already showed that ( and it is not much longer)
I am still not sure that it is safe to do it as the consequences are great (it is my money)
I will program my HP to reduce fan speed during DF, for a number of times at 50% CFM then reduce to 40% and so on.
During this testing It would prudent to monitor important parameters, please advise which and I will set it up.
Thank you everyone for your help. Especially mad fridgie-- for all your time and frustation.

regards

pilko

[mad fridgie]

I will now talk about the possible risk.
When the fan is not running the amount of energy pick up is very low (this you understand), what can happen, instead of the liquid being boiled off, some liquid may leave the indoor coil. (this very specific to your machine, and i can not help here) the liquid can not be compressed, so could hydraulic your comp internals (highly unlikely), but it could dilute your oil, which will reduce the lubricating effect. (additional wear on bearings ect.) The amount of refrigerant flow is determined by the outdoor coil pressure, which should be low, but (not in your case) if timed defrost only this pressure could rise, forcing more flow through the indoor coil, and the type and size of the expansion device. (TEV, Capillary, EEV, fixed orifice)
The accumulator that you do not have, traps any liquid prior to entering the compressor.(this the mechanical limits of your system)
OK so far!

[pilko]

I'm Listening and understanding.

[mad fridgie]

It is possible that when the defrost is complete, (starting to pre -heat, still no fan) then when the fan starts a puff of stream my come out, not that this really a problem, just people maybe unaware and think it is smoke.

[pilko]

Now that I have a better understanding, can I get back to my original question, phrased in a different way?
Proposal:-
--Install tank in vapour line as shown.
--Tank water collects heat during heating mode (I realize that is heat not going into living area.)
--Tank will eventually reach close to vapour temp.
--During defrost, stop the indoor fan the buffer coil will now replace the indoor coil and become the evaporator.
--The compressor will be happy.
--No more cold air into my living area.

pilko

[mad fridgie]

Reply to latest "Hvac-Talk" (please forward)
Carrier.
if one brand can defrost with out a fan running, then this means the "energy mass balance" would work for all.
So the "Pros", are all wrong for the reasons given.
Mechanically the USA brands may have problem, due to chance of liquid entrapment in suction line (Accumulators do not seem to be standard)
Controls are also likely to be very poor.
Tech was limited to a level which should be understandable.
The USA has had it to good for too long, installing 15Kw heater bank to cover defrost, yes it works, but masks basic fundamental flaws. Only now are is the common man looking into energy saving. You are behind most of the world in this area. Learn from those with more experience and knowledge in this subject.

[mad fridgie]

Now that I have a better understanding, can I get back to my original question, phrased in a different way?
Proposal:-
--Install tank in vapour line as shown.
--Tank water collects heat during heating mode (I realize that is heat not going into living area.)
--Tank will eventually reach close to vapour temp.
--During defrost, stop the indoor fan the buffer coil will now replace the indoor coil and become the evaporator.
--The compressor will be happy.
--No more cold air into my living area.

pilko
No many other issues to contend with.

If you want to change your system, go to hot gas defrost with a buffer in the comp discharge line.
You still need an accumulator!
Nothing to do with the indoor unit.

[pilko]

Can you explain in simple terms why the heat in the buffer tank, transferred to the buffer tank coil cannot do the job of the "A" coil during defrost.

pilko

[MikeHolm]

OK, here is a pic of the coil. I don't know if "A" coils are used outside North America.

8374

[pilko]

Thanks Mike. I know what an "A" coil looks like.
I think I am not explaining myself properly.-- my proposed is a tank of water with a heat exchanger in it.
The Heat exchanger/coil will do the job of the "A" coil during defrost, since the "A" coil cannot satisfy the heat requirement during defrost.

regards

pilko

[mad fridgie]

In simple terms, the vapour will be very highly superheated, which in turn cause very high discharge temps (damage to compressor)

[mad fridgie]

"A" coil can satisfy the defrost requirement.

[MikeHolm]

Thanks Mike. I know what an "A" coil looks like.
I think I am not explaining myself properly.-- my proposed is a tank of water with a heat exchanger in it.
The Heat exchanger/coil will do the job of the "A" coil during defrost, since the "A" coil cannot satisfy the heat requirement during defrost.

regards

pilko

The coil pic was for Mads info, not sure if they use ones shaped like that down there.

[MikeHolm]

"A" coil can satisfy the defrost requirement.

It is the interior coil

[mad fridgie]

Thanks Mike,

This design of coil is not common in this neck of the woods.
Generally more long and skinny (long and no so high) and usually comes as package (fan included in the housing)

[MikeHolm]

These ones are meant to sit above a forced air heat exchanger. Pretty archaic in my opinion. (the furnace, not the coil)

[pilko]

Just calculated the area under the hot vapour line temperature curve for the two defrost conditions,930
and 590 CFM.(blue lines)
Since the areas under under the curves are proportional to heat (dT x Time) I thought it would be interesting
to compare the two quantities of heat that were transferred from the "A" coil to the compressor.
At 930 CFM, heat transferred = 641 CFM
At 590 CFM, heat transferred = 632 CFM
In other words, just as much heat is transferred in both cases.
This is further confirmation of your argument.
My concirn is the final temperatures at the end of defrost -- 10*C at 930 CFM and 4*C at 590 CFM.
What Is the minimum safe temperature for the compressor???

pilko

[pilko]

Cannot figure out how to edit my post.
The heat transferred units should be *C.Minutes not CFM.

[mad fridgie]

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.

[mad fridgie]

8382

This how you do it if want to shorten defrost time, and have energy benefits from the defrost.

[mad fridgie]

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.

[pilko]

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

[mad fridgie]

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

[pilko]

"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

[mad fridgie]

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

[pilko]

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

[mad fridgie]

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.

[pilko]

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

[mad fridgie]

Yes it would work, but is not energy efficient! You are stealing energy from the house, worse than turning the fan off.

[pilko]

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

[mad fridgie]

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!

[mad fridgie]

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.

[pilko]

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.

[MikeHolm]

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.

[richardb14]

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.

[richardb14]

I should also point out that Danfoss now own thermia!

[pilko]

@ 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

[Emmett]

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!!!

[mad fridgie]

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.

[MikeHolm]

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

[mad fridgie]

Hi Mike, have a look on HVAC TALK, for me please "I have been banned."
any comments from them
search barbar.

[MikeHolm]

Will do, I haven't been able to register on it as it keeps kicking me out. I will try to re-register tonioght.

[mad fridgie]

You are a bad boy as well. Get to the back of the room with me.

[MikeHolm]

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...

[Emmett]

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.

[MikeHolm]

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).

[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

[mad fridgie]

@ 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.

[pilko]

Thanks mad fridgie,
There will be some frost tomorrow morning, so will check the accumulator and if OK, will do some testing then.

pilko

[MikeHolm]

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.

[pilko]

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

[pilko]

No weather bomb and none forcast.

BTW How do I edit a post?

pilko

[pilko]

@ 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

[mad fridgie]

Well covered, go for it!

[pilko]

Thanks mad,

Forecast a bit of frost overnight. Will give it a try in the morning.

pilko

[pilko]

@ 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

[mad fridgie]

How did it feel in your house?

[pilko]

@ 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

[MikeHolm]

Does this mean that only compressor heat is being used for defrost? Pilko, are you wanting to make the tank storage as well?

[install monkey]

mike ur dragging this post out arent u- just pop to pilko's and have a maul with his kit! or are u trying to get a sticky post haha

[MikeHolm]

I'm dropping in at Xmas with a pint or two of cheer. Were are no where near a sticky anyway, haha.

[pilko]

@ Mike,
"Does this mean that only compressor heat is being used for defrost?" --- also the heat in the lines,the vapour in the "A" coil and the "A" coil itself."

are you wanting to make the tank storage as well?---only if the outdoor coil fails to defrost completely.

pilko

[MikeHolm]

i guess you will have to see how it works without the extra heat source of the the room air. The other possible benefit of a tank (Mad, correct me if I am wrong) is that some of the tank heat could be used to do some floor heat if desired.

[mad fridgie]

The coil is not defrosting using the compressor energy only (energy is still coming from the system)
Hot gas defrost, is more a compressor only defrost.
Using energy for more than one application, really means you study the applications to design the right system.

[pilko]

UPDATE,

Had 12 Defrosts with indoor fan stopped ---everything OK,

Writing some code to stop fan automatically at defrost start and restart fan when "A" coil temp >40*C.

pilko

[mad fridgie]

Great news!
I am not normally into one up-man-ship, but in this case i think the "Pros" on HVAC TALK need to be told of your results.
In this industry things are very rarely black and white, so for one of the "pros" to say i was "wrong" was just pure arrogance and ignorance of the fundamentals.
Others gave opinions based upon what they know and seen, and that is fair comment.

[pilko]

@ mad fridgie,

If I respond to the other forum now, he will probably tell me that it is "OK for now but the compressor will
fail after a short time"---- so, I would prefer to give it more time and be able to tell them that it has been OK for a month for example.

pilko

[MikeHolm]

I'm still unsure where the heat for defrost is coming from. I can't see enough heat from the local piping so there must be a high percentage of compressor heat going through.

[MikeHolm]

Mad, I haven't see and "barbar" posts on the HVAC forum

[mad fridgie]

Hi Mike,

good question.

What is the weight of the "A"coil and what temp is it, what is in the coil (hot refrigerant), you also have the interconnecting piping, and of course the mass around the all this. So you could work out the energy in all this. This energy is also is pumped (compressor uses energy) so the combination is rejected into the outside coil to melt the ice.

Reply on HVAC TALK, were removed and I got banned for a few weeks (Thats the rules, which I did break)

Pilko, fair comment

[pilko]

I'm back,

I am still defrosting without the indoor fan and everything is OK.

I just posted the following message on the other forum:-

"Update:-
I have been defrosting with the indoor fan shut down for the past 5 weeks . (approx. 120 defrost cycles). It works fine and I have had no problems.

pilko."

[mad fridgie]

Good news
more comfort and less power

[mad fridgie]

This a reply form HVAC-TALK
"Quote:

Originally Posted by pilko http://hvac-talk.com/vbb/images/buttons/viewpost.gif (http://hvac-talk.com/vbb/showthread.php?p=12188321#post12188321)
Update:-
I have been defrosting with the indoor fan shut down for the past 5 weeks . (approx. 120 defrost cycles). It works fine and I have had no problems.

pilko.




I've been reading through this thread & though I haven't read it all it is a lot more interesting than I thought it would be. Any HP manufacturer or tech support would say as a fact that the indoor blower should always run during defrost & I would agree. You have evidently done significant research & found some conflicting data to support the alternate view which most anyone who works on HP's would disagree with. You have to remember HP's are designed for a variety of climates & yours may be such that a defrost is not needed very much so you mat be able to get away with stopping the blower while someone in another climate may not. There is no question that stopping the blower motor during defrost will lower the added cooling btu's entering the structure & also lower power consumption during that time but it also will make the defrost less efficient if it is really needed. Also compressor flooding should be a serious concern.
__________________
Gary
-----------"
I wonder if you could forward this response.

Thanks Gary, for being a little more open on your thoughts.
It would seem that only North American heat pump systems continue to run the indoor fan on defrost, much of the rest of the world, turn off all the fans during defrost. These system are designed to run as low as -15C ambient. This is limited to refrigeration compression ratio limits, and not defrosting limitations.
Your concern on flood back is valid, in this case total charge and size of the suction accumulator was taken into consideration. Liquid flood back would not occur. How ever vapour at saturation may enter the compressor, but this is not really an issue, as the refrigerant passes over the comp motor, picking up sufficient superheat to ensure that oil dilution will not occur for the short defrost period.
Technically there is no reason why all systems in your neck of the wood s can not be converted, but there are practical limitations, such refrigerant distribution (primarily the out door coil), defrost sensor position and general control scenario. How do we determine defrost efficiency, defrost should be slower without a fan running (less energy picked up from the evap), so it would be fair to say efficiency is less, but if we include the energy to recover after defrost, then defrosting without a fan is more efficient.
cheers
mad fridgie (barbar)

[pilko]

Thanks Mad,

I have posted your / my response on the other site.

Regards

pilko

[mad fridgie]

Quite a few rude answers on the other site.
It would be quite nice to know what sort of energy savings you are making.
Maybe you could be on to a winner converting systems. When you do, and make your millions, do not forget poor mad fridgie, at the bottom of the world.

[MikeHolm]

Quite a few rude answers on the other site.
It would be quite nice to know what sort of energy savings you are making.
Maybe you could be on to a winner converting systems. When you do, and make your millions, do not forget poor mad fridgie, at the bottom of the world.

You are only upside down, not on the bottom of the world

[mark957]

I think you could install another external heat exchanger that will be replacing the internal one at the time of defrosting.