Defrost without the indoor fan

[barbar]

Hi I have been assisting Pilko on setting up his defrost system
http://hvac-talk.com/vbb/showthread.php?t=978262
There seems to be a lot of resistance to the "no fan method."
There was a suggestion that Pilko should come out of retirement to teach you engineers.
If you want to be taught then I am willing to teach those who are willing to learn.
barbar (aka, mad fridgie, Refrigeration Engineer.com)

[amd]

Defrost without the fan?

Where's the heat to melt the ice supposed to come from?

The heat absorbed by the refrigerant in the compressor isn't sufficient.

[barbar]

Defrost without the fan?

Where's the heat to melt the ice supposed to come from?

The heat absorbed by the refrigerant in the compressor isn't sufficient.

It is my understanding that the system in north america are "reverse cycle" and not "hot gas" defrost, there fore your total energy required for defrost comes from a combination of residual energy from the components of the system (primarily the indoor coil, and the compressor) and the energy drawn by the compressor during defrost. There may not be much heat (temperature) but there is sufficient energy above the freezing point of water to defrost.
(check results on http://hvac-talk.com/vbb/showthread.php?t=978262 )

[BaldLoonie]

Look at the 4 page thread on this subject in AOP residential. No need to start a new one here.

[barbar]

Look at the 4 page thread on this subject in AOP residential. No need to start a new one here.
I was unable to comment on that thread, It is very basic in technical information. (as comment was made) The OP of that thread is not a refrigeration engineer.
Most replies from the pros, simply had no technical back up around the comments and in my opinion where totally wrong on a fundamental level, however your systems may have practical limitations that do not allow for this type of defrost. If so what are they?
I opened this thread up so a technical discussion could be made to all that are interested and all could comment to what ever level they are up to.
This industry is not black or white, it is grey. so to encourage learning differing opinions have to be aired.

[jpsmith1cm]

barbar,

technical discussions here take place in the Pro's Technical forums.


You seem like a knowledgeable guy and one that I'd like to see as a Pro here.

The requirements are in my signature. I'm sure you meet them but for the post count, which you could easily remedy.

[barbar]

barbar,

technical discussions here take place in the Pro's Technical forums.


You seem like a knowledgeable guy and one that I'd like to see as a Pro here.

The requirements are in my signature. I'm sure you meet them but for the post count, which you could easily remedy.

Thanks JP,

when post are met, we will see if you want me on board as pro.

cheers

barbar

[Failure2Comply]

I don't understand how limiting the heat gain from the indoor coil during defrost would help?

[barbar]

I don't understand how limiting the heat gain from the indoor coil during defrost would help?
That is a good and fair question, if we looked at the defrost part only, then reducing the energy gain from the indoor coil, does reduce the effectiveness of the defrost (Speed or length of defrost), how ever if the fan is on, you are removing energy from the home, (and a cold draft), this energy does need to be replaced, I believe it is common that you have a heater bank, that over comes this problem. But is this efficient? "No"
Why is it not?
During defrost and the fan is running, your cooling system COP is very high (little power draw, for lots of cooling), this is due to the fact the condenser saturated pressures are very low (defrosting the outdoor coil). When you revert back to your heating cycle, the heating COP is not has high,as it was in the defrost cycle. So the net effect is that you need to introduce more electrical energy, to recover the losses made during defrost.
So here is a very simple example (no too techie)
Your heating COP is 3, or in other words you introduce 3kws of energy into your home by using 1Kw of electrical power
On Defrost your cooling COP is 6, or in other words, we remove 6Kws of energy from your home using 1kw of electrical power.
So keeping the maths simple, we have removed 6Kw for 1Kw, which has to be replace which is 6Kw for using 2Kw, we have wasted 1Kw.
Practically defrost will be a bit long, and the thermal mass of the indoor unit will be colder, so the actual saving would not be 1Kw, but slightly less.

[amd]

Melting ice a fairly energy intensive. (144 btus per pound) I still don't know where the heat is supposed to come from if the fan is off.

Compressors produce heat due to compression and motor losses, but the cop is 1. (total lifespan of compressor might be reduced due to wear of defrosting like that, longer defrost cycles also reduce the total amount of heat the heatpump can capture, increasing heat strip use)

Heat strips also have a cop 1.

I also don't know where you got the 6 COP figure during defrost cycles; with a very cold outdoor coil, the odds of actually have a solid liquid column of refrigerant feeding the indoor coil are low.

I don't think there's a point of playing silly games:

There are much better ways to reduce energy losses associated with defrost cycles:

- Install a demand defrost board to eliminate unnecessary cycles
- Install an outdoor stat to keep the second stage of heat strips off above a certain outdoor temp) -->Temper the air, don't heat it.
- Keep the outdoor coil clean so it doesn't run as cold in heating mode -->less frosting

[barbar]

Ok good points.
YOU pick a standard unit used in north america, but you must know how the system works and not rely on the sales BS, pressures, temps, air flows, current draw power factor, compressor displacement.
We will work out firstly your ice production (what is required to be defrosted)
I use Copeland Select7, so any figures I quote as being technical will be referring to this.
Do you think this is a new concept? It is being used just about in every other part of the world, for at least 20 years, and for temperatures down to -15C (more modern ones down to -20C)
You do not understand the process, so you think it is a silly game!
I do agree that smart defrost control is important "defrost on demand" and good service!
Aux heaters we design for 5% days, which normally equates to a max run time of less than 2% of the heating season, what is the point of designing a heat pump system if much higher than this.
Some data Copeland ZR32 on R22
start of defrost (indoor loaded with liquid refrigerant, outdoor frozen with ice) fan running
27C SCT and 12.5C SST, cooling duty 7.7Kw input power 0.8Kw "COP 9.32"
during defrost
27C SCT and 5C SST, cooling duty 6.1kw, input power 0.9Kw "COP 7.14"

I was pretty conservative with my 6
However I would say the SCT would be lower that 27C, but Copeland indicate that this is out of range, so no data available. i could just go down to fundamentals, but then the info would not be independent.
The lower the SCT the lower the draw, but the SST would track down due the expansion device limitations. COP would still remain high.

[barbar]

If you took a pretty standard unit heating 3.5Ton 12.3Kw, say an average COP of 3, then the cooling capacity would be around 8.2Kw
If the air ambient was 3C at 100% RH, and chilled to 0C with an evap temp -5C, you would produce 5.2Kgs of ice (presume no by-pass or water drain)per hour (11.5lbs give or take)
If you defrosted every hour, you need 0.5Kw (1650Btu) to defrost this ice. Of course you need some energy to bring up the coil block itself.
If we just for time being forgot all other energy apart from that of the compressor during defrost. This unit normally would draw around 4Kw, but during defrost, the drew would drop (low SCT) by approx 30% (check on compressor charts), so draw would be around 2.8Kw. Therefore we 0.5Kw for defrost we have 2.8kw available defrost will be 0.5/2.8 18% of an hour 10 mins. Of course we do have the residual heat from the system, which will speed it up.

[amd]

"You do not understand the process, so you think it is a silly game!"

Tell me where the heat to defrost the coil comes from. :p

Having the heat come from the compressor isn't more efficient than using heat from the conditioned space and compensating with aux strips.


Aux heaters we design for 5% days, which normally equates to a max run time of less than 2% of the heating season, what is the point of designing a heat pump system if much higher than this.

Is cooling a factor there?

In north america, if heatpumps were sized to provide sufficient heat at design, they would short cycle like crazy in cooling mode. The airflow requirements would also be ridiculous.

Even if the strips provide 50% of the heat, running a heatpump with a cop of 2-3 can make sense if there isn't a cheap energy source available (like gas) and cooling is needed anyway.

Maybe north american equipment is obsolete compared to what you have in europe - central models with inverter driven compressors are very new to the market here.

[madblack]

Interesting method , sounds like you have done a lot of homework too , in systems that use this method , what is the sequence of operation after defrost termination ? (I would imagine that a large pool of very cold air is sitting in the plenum etc)

[barbar]

Cooling is not a biggy where I live, but in other parts, cooling is as big as heating.
Fixed speed machines will always cycle, it pretty hard to design to cover all eventualities.
As in parts we go from 40C to -10C, so house loads vary dramatically.
For air to air systems, inverters or digital generally can not be beaten, as capacity meets load.
We generally have less airflow for heating than cooling, but this comes down to the wind chill factor, a warm dry wind feels cold, so we tend to have a lower volume at a higher temp.
I am in New Zealand, but our engineering is typically European and Asian.
In my opinion, North america becomes a leader in a field (as it was in the HVACR), then just sits on the technology for way to long, to the point it becomes obsolete as you say.

[barbar]

Interesting method , sounds like you have done a lot of homework too , in systems that use this method , what is the sequence of operation after defrost termination ? (I would imagine that a large pool of very cold air is sitting in the plenum etc)
Excellent question!
Yes of course the indoor coil and its surrounding will be colder than you would normally expect. After termination, the refrigeration cycle returns back to heating mode, however the indoor fan remains "off", only when the indoor coil reaches a temperature above 40C(upto 50C), then fan is then brought back on, with a ramp if possible. This way you do not get the cold draft.

[madblack]

I am going out on a limb that for a delay period after termination the indoor fan stays off to reheat the coil,plenum etc, and after a suitable delay (or temp rise) the fan restarts. I get the change in performance due to reduced CR , and am starting to get that the plenum rewarming process also starts at a greatly reduced CR as well , so all in all sounds pretty cool , Trouble is Industry in North America has huge Inertia that resists new methods (not a reason to avoid change, just sayin is all). I think this Idea is worth putting side by side with a conventional system to test different strategies and see what happens . I have the unique situation to be able to both Research and teach at the same time , so even if it was not especially productive , the learning process would still continue.

[madblack]

Guess it was a sturdy limb....!!

[barbar]

Hi madblack, i am best known as mad fridgie, good to be "mad" ye!
This came about from one of your country men asking about installing a buffer tank on another site.
(check my first entry and follow the link on this site)
Apart from the backbiting, Pilko has recorded some good data. (not the way i would do it but all the same is excellent)
It is easy to get stuck in our ways and use rules of thumb, but with worldwide changes in energy use, a lot of what was normal is going out of the window, i feel as an industry worldwide that we need to retrain ourselves, to bring us back to the pinochle of the trades field that we once were.

[barbar]

Guess it was a sturdy limb....!!
Very sturdy indeed, I now:grin2:

[madblack]

.
[/QUOTE]I am in New Zealand, but our engineering is typically European and Asian.
In my opinion, North america becomes a leader in a field (as it was in the HVACR), then just sits on the technology for way to long, to the point it becomes obsolete as you say.[/QUOTE]
That may be cuz one of our favourite quotes is "if it ain't Broke , don't fix it!"
but on the other hand, there are also a lot of innovators as well , but its hard for them to be heard at times. Could you (if it isn't against the rules post some brand , model , or link info for equipment that uses this system? I for one would like to see some of the product specs if something is in production.

[barbar]

Well it something we do not think about as has been standard for years, all the Japaneses units work this way, but they all pretty complicated, inverter this, modulating that!
Here is a New Zealand manufacturer, pretty good, basic equipment, a good few steps up from what you are describing but a bit behind the Japanese (this company is now in the 21st century)
http://www.temperzone.co.nz
It may not have the info you require, as i said we take it for granted!

[madblack]

Thank you Barbar I am sure now that i am aware of this type of defrost system I will be finding them all over the place, as a kind of inventor/putterer myself I am fascinated with the off beat , the standard can be a little boring. Once I get a little more used to the protocol around this forum , I would like to chat more with yourself and also Pilko , it seems the research end of things is his bag as well.

[amd]

High end variable equipment probably gets crippled when set up by the average installer or tech in North America - that's something to consider.

I'm for ecm motors, two stage gas valves on furnaces, and conventional heatpumps when used in the correct applications - but above and beyond that, the simpler, the better.

[barbar]

High end variable equipment probably gets crippled when set up by the average installer or tech in North America - that's something to consider.

I'm for ecm motors, two stage gas valves on furnaces, and conventional heatpumps when used in the correct applications - but above and beyond that, the simpler, the better.

Ah the installer, normally speaking this defrost method is some thing the manufacturer incorporates into the controls, and should not be an issue.
Saying that I know stupidity has no limits.

ECM motors for sure, gas valves do not know "do not do furnaces", for fast acting systems (air), i do think some level of smarts are required, for slow acting systems (underfloor or thermal storage) simpler the better. "on/off"

[madblack]

I quite agree AMD , I don't think I would be inclined to expiriment much with it either , could get expensive , but given a couple of safety factors , like suction accumulator , indoor coil TXV and some amp monitoring , an excircise like Pilko in undertaking is how big advances get made in a great field . I once set up my old carrier HP in Canada on a DDC controller for total defrost control , unfortunately it was too soon in my carreer and making a living kept getting in the way! Cheers !!!

[garyed]

I've been interested in this blower-less defrost since I read the thread in the AOP forum that mentioned it. I'm sure that if I stopped the blower motor on my system at home that it would not make it through the winter without freezing up solid. Our design winter temp is 29 degrees F. but we do have a lot of humid weather so what I want to know is what is different about their defrost design than ours. The whole reason for stopping the outdoor fan is to build up more heat faster so it seems that stopping the indoor coil would offset some off its benefits. I'm not against the idea, I just want to know the specifics of how it works & the different types of controls that are used to make it work.

[madblack]

I am new to this too , but having beaten this horse at the control board level a bit I believe the secret may be in the precise detection of a need for defrost firstly, and secondly the need (for defrost)must not be allowed to become too severe (due to the limited heat capacity of this type of defrost) . Precise management is required , rather than enableing defrost based on only pre-set accumulated runtime and one klixon sensor. I realize that modern NA systems are alittle more sophisticated than this , but are still pretty "one size fits all" . I know this hasn't worked that great for me anyway.....

[barbar]

Basic control, is based around a temp time initiation, when the outdoor coil reaches a predetermined temp, then unit continues to run for a preset time, defrost starts. When the coil heats up to a preset temp, defrost is terminated. (the better the system the more of these levels come into play) Many have tried true defrost on demand, measuring the actual ice thickness, but I have not seen one that works satisfactory 100% of the time (so even these have some level of temp time backup)
OK you have to ensure that liquid flood back does not occur, easily solved with the correct accumulator.

[barbar]

On Post 12, I have shown quite bad conditions for true coil freeze up (blocking airflow, not just looking frosted, which happens when at -10C ambient)
Also do not consider the problems that occur when your filters are blocked, which indicated low airflow for defrost. This can cause irregular freezing of the outdoor coil (when in heating mode), and premature defrost termination. (high temps and pressures) Once ice is formed due to fault generally standard defrost will not clear it.

[garyed]

Basic control, is based around a temp time initiation, when the outdoor coil reaches a predetermined temp, then unit continues to run for a preset time, defrost starts. When the coil heats up to a preset temp, defrost is terminated. (the better the system the more of these levels come into play) Many have tried true defrost on demand, measuring the actual ice thickness, but I have not seen one that works satisfactory 100% of the time (so even these have some level of temp time backup)
OK you have to ensure that liquid flood back does not occur, easily solved with the correct accumulator.


That sounds like a typical time temp defrost system. I'm not clear if the defrost terminates only on temp or is there a time override that will only allow defrost for so many minutes whether the coil reaches temp or not.

[amd]

Defrost terminates when the coil gets above a certain temp or the maximum time has elapsed - whichever comes first.

[barbar]

amd, is basically right.
Most manufactured units have their own defrost controls, so each has there own bag of tricks.
Early issues arose from sensor position, but this seems to be no longer an issue.
I would suspect that with the fan on, and a fast defrost, that you practically over shoot by quite a way your coil temp termination set point.

[garyed]

Defrost terminates when the coil gets above a certain temp or the maximum time has elapsed - whichever comes first.
I know that's how our systems work but I wasn't clear if barbar's system is designed any different. Most of the ones I work on terminate defrost around 10 minutes if the sensor has not reached cut off temp. Some are a little higher but I don't know of any that will allow more than 15 minutes. I would just assume that with the blower not running you would need longer defrost times to compensate for less heat at the outdoor coil. It really comes down to a comfort & numbers game. If you can save money & save comfort then that is a good & logical way to go. If not then it doesn't make sense. What I still don't get is if it works well, then why haven't US manufacturers done it that way even with their high SEER units. It's not like it costs considerably more to
implement & it would also be a great sales tool for the equipment so what am I missing?

[barbar]

Maybe we should look at why this system in not implemented.
I would say leaving the fan on and have Aux heaters running is slightly more robust, in ensuring defrosts (for the reasons all have mentioned, you will have more energy available)
The units here are totally packaged, "come complete as a set" outdoor unit, indoor unit that incorporates the coil and fan, so the system is balanced, so there is less likelyhood, of install errors. In the states, who supplies the the different components, is the fan supply separate to the heat pump supply?

[garyed]

Maybe we should look at why this system in not implemented.
I would say leaving the fan on and have Aux heaters running is slightly more robust, in ensuring defrosts (for the reasons all have mentioned, you will have more energy available)
The units here are totally packaged, "come complete as a set" outdoor unit, indoor unit that incorporates the coil and fan, so the system is balanced, so there is less likelyhood, of install errors. In the states, who supplies the the different components, is the fan supply separate to the heat pump supply?

In the states each piece of a split HP system is purchased separately. It is of course advised to install a complete matching system but the individual pieces are sold separately. In some cases the Air handler & Outdoor unit are purchased together & sometimes not. Some times just the indoor coil is purchased with the outdoor unit & in some cases the indoor & outdoor pieces are not even made by the same manufacturer. That being said anything but a factory matched split system heat pump is frowned upon in our industry but there is still a lot of mismatched units working fine for a lot of years.

[barbar]

In the states each piece of a split HP system is purchased separately. It is of course advised to install a complete matching system but the individual pieces are sold separately. In some cases the Air handler & Outdoor unit are purchased together & sometimes not. Some times just the indoor coil is purchased with the outdoor unit & in some cases the indoor & outdoor pieces are not even made by the same manufacturer. That being said anything but a factory matched split system heat pump is frowned upon in our industry but there is still a lot of mismatched units working fine for a lot of years.
It could well be that this fact, does stop the use of the no fan method.
If for instance you have an outdoor unit and mismatched indoor unit (larger and a lot of airflow), then your condensing pressure pressures will be very low, your outdoor coil, will freeze more easily and likely unevenly.
In the very basic systems, problems can occur with defrost (no fan running) when the internal house temp is very low, the better systems overcome this by changing the speed of the indoor fan, 2 benefits, no wind chill issues and elevated discharge pressure, so increase residual heat within the indoor coil which aids the defrosting (most systems run this way nowadays).

[John Markl]

Maybe we should look at why this system in not implemented.
I would say leaving the fan on and have Aux heaters running is slightly more robust, in ensuring defrosts (for the reasons all have mentioned, you will have more energy available)
The units here are totally packaged, "come complete as a set" outdoor unit, indoor unit that incorporates the coil and fan, so the system is balanced, so there is less likelyhood, of install errors. In the states, who supplies the the different components, is the fan supply separate to the heat pump supply?

Most heat pump air handlers have the elements AFTER the coil, so running the elements wouldn't necessarily create "more energy available", would they?

[barbar]

Most heat pump air handlers have the elements AFTER the coil, so running the elements wouldn't necessarily create "more energy available", would they?
If the fan is running, then there is more energy available, and if you control you elements to replace the energy that is lost during, then again you will have more energy available compared to that of not having the fan running

[madblack]

I have always thought that keeping the system(fan wize anyway) running during defrost was a little daft, especially considering the added strip heat to keep Mrs Joneses feet warm. I have often thought that a split outdoor coil could work , able to defrost itself! , yes a bit of a control nightmare but efficient. Oh well , maybe when i retire I will have time to play with it...

[madblack]

In the meantime I am enjoying a Snow day at home, Cheers.

[barbar]

I would of the thought a retro fit, technically is esay, but practically is more difficult, need control wiring for the fan, ( I not sure of the logistics of your control boards and the like),
I would ensure that the suction Accumulator is the correct size to ensure liquid flood back does not occur.
I believe Pilko has 2 standard system running this way in Canada (only control mods made)