R22 Geo Heat Pump 3

[TomHussey]

I am seeking information regarding an R22 based geo-thermal heat pump. I have limited knowledge of refrigeration but wish to be on top of required service. The manufacturer no longer exists and little information was provided.

The system is an integrated unit. A plate inside specifies R22 "test" pressures of 150psi for the low side and 300psi for the high. Does this mean that under normal operational condidtion these pressures should be present?
The compressor discharge measures 46C while the suction side is just under 0C (frost covers the top of the compressor). I have been told that R22 should not be run below freezing, yet the tables from Dupont show properties down to -46C.

How can I determine if/when/what service is necessary?

 

[willard3]

What do you mean by service?
Do you mean electrical branch circuit size?
Do you mean refrigerant service?

Here is a pressure temp chart for r22

http://www.longviewweb.com/pressure.htm

Here is a pressure/enthalpy chart for r22

http://hvacsuite.com/R-22_Enthalpy_chart.pdf

 

[MintJulep]

No telling what "test pressure" really means, as there is no inherent meaning to the term. But no, I would not expect those pressures in "normal" (whatever that may be) operation.

If you are measuring the temperature of the discharge pipe then there is a certainly some amount of superheat in that measurement. The corresponding pressure is well below the placarded 300 psi.

I can't think of any valid reason why R22 can't be below freezing on the suction side. R22 is commonly used for refrigeration and freezers with evaporator temperatures well below freezing. Obviously you don't want a wet coil below freezing, but that has nothing to do with the refrigerant.

So, how will you know when this thing needs service? When it stops working it's probably because something broke.

 

[TomHussey]

Thanks for the quick replys...

In answer to Qs:

-By Service, it seems to me that the unit is not operating with good efficiency. The secondary heat is on with a high duty cycle at outside temp -10C. Second heat starts up when the outside temperature is about 0C. I believe that the unit may be operational but not charged or configured correctly. I want to understand what I need to ask the person I contract to service it for.

In my case, the coil is in moving water. It is not frozen up and I can see a temperature reduction from the water in to water out (10C down to 6C).

Frost covers the whole top of the compressor and pipes leading from the evap coil.

Can I tell from the charts if the unit is correctly charged? I assume that the fill would be R-22 as per the plate. I will read about "super heat" now.

My end goal is to improve the performance/efficiency of the unit.

Thanks again,
Tom

 

[MintJulep]

Has the performance changed, or have you just started paying attention?

No, you can't tell from the refrigerant charts alone if the thing is properly charged. Definitely not with only pipe temperature measurements. With pressure and temperature you could determine super heat and sub-cooling at various points, and get a reasonable idea of what is happening. Still, you really need access to the manufacturer's design and operating data to know what it is supposed to do.

One of the things about refrigeration systems is that everything always balances out. The temperatures you've given (although you don't have much to go on) are all "about right" - because they have to be. That is, a 6C leaving water temperature and a 0C suction temperature are a reasonable combination. A 46C discharge temperature isn't out of whack, and making an assumption about the super heat at the compressor discharge, the discharge pressure is reasonable for a 0C suction pressure. No way to tell if that is the expected design operating point however.

Note also that (assuming that you are in the US) unless you are a licensed refrigerant tech you cannot legally connect a set of pressure gauges to the system.

 

[TomHussey]

Thanks for all the information. I am in Canada, but still do not intend a DIY fix. I am sure it will be better to get a pro to work through the issues.

One web page I looked at suggests the installation of a thermostatic expansion valve in place of the fixed valve that the system has. Is this a good idea for increasing the efficiency?

Thanks,
Tom

 

[MintJulep]

An expansion valve allows the system to accommodate variations in evaporator load.

In theory at least, the evaporator load of a geothermal heat pump should be almost constant.

So no, I wouldn't expect an expansion valve would do much for you.

 

[berkshire]

TomHussey,
The only way you can be sure of what is going on with your heat pump, is to put a set of gauges on it and measure the temperatures and pressures at the same time.
Your heat pump should have a crankcase heater on the compressor and although the top of the compressor and the inlet may have frost on them, the center of the body of the compressor should be frost free.
Get a pro in to look at it, if only for your own peace of mind.
B.E.
EPA licenced.

 

[hollandhvac]

The test pressure is the pressure of the dry nitrogen that needs to be put in on the low side and in the high side to check if the pipe work is made correct and can withstand the pressure of the refrigerant that will be put in afterwards. The 150 PSI on the low pressure side and the 300 PSI on the high pressure side are standard figures.

That Dupont shows lower property's than below freezing is just because they tested these refrigerants in the laboratory.

By the way why are you using R22, it is going to be replaced by more environmental friendly refrigerants?

 

[TomHussey]

I will be getting the unit inspected and tested, but I want to get it set right the first time.

Should I consider changing the refrigerant to one of the newer tech gasses? The efficiency is not good now, will this help? What changes in the rest of the system will be needed (huge question). I would need much more design data than is available to me if large changes are needed. If I increase the heat transfer too much there is a risk of freezing the evap side (which is warmed with moving water). If there is no leak, wouldn't it be better to keep the R22 in place?

If there is a crank case heater it must be internal to the compressor. I believe it is an 8 ton system, compressor runs on 240VAC. It has a capacitor to increase startup torque. I think this is all quite standard for this sort of equipment

Thanks,
Tom

 

[MintJulep]

How old is the system?

R22 will be available for service needs for another 10 years.

None of the currently available replacements for R22 will increase performance of the system. At best you could hope for the same performance, but probably it would be less.

With the limited information that you seem to have there is really nothing more than generalities that we can suggest. You can't have the only one of these things in existence. Try to find some detailed information.

 

[willard3]

If you change refrigerant, you will have the wrong evaporator, condenser and compressor....maybe also the wrong lubricant.

The efficiency on any heat pump will be less than 30% as it is a Carnot cycle. Carnot cycle works best when delta t = 0; the farther you get from that, the less efficient they are. Just because you don't pay for the heat source/sink, efficiency doesn't increase....the short-term costs will decrease.

 

[berkshire]

Tom Hussey
I just did a study for a customer on switching a set of R22 heat pumps to a new set using Puron R410. The good news was that by switching, he would save $80 per month on the greater efficiency of the units. The bad news was, that due to the capital cost of the new equipment ( new pumps, new coils, new air handler etc..), the payback period was 7 years.
So based on that, I would suggest waiting for your equipment to wear out or break before upgrading.
B.E.

 

[CRG]

Tom, you stated "The efficiency is not good now." So this begs the questions:

when was the efficiency good?
what was the efficiency when it was good?
what is the efficiency now?
how do you know that the efficiency is not good now?

 

[TomHussey]

I am no expert in refrigeration, but will do my best with your questions...

In doing a comparison of resistance heat vs the heat pump, I find that the system is not saving much if anything. In this I have estimated the pumping power for water (that the heat is removed from) and the power used in the compressor. This gives a heat rise that I compare with resistance heat. If the system was working, I would hope the energy taken from the water would be significant.

I know a little more about the system after researching a bit (this is probably too basic for the folks here). The high side is connected to a heat exchanger that heats the indoor air. This condenser is then connected to a heat exchanger housed inside an accumulator. The outflow from the heat exchanger is routed to a manifold and to three capillary tubes. These capillary tubes feed a large evaporator. The evaporator output enters the accumulator and then back to the compressor.

I need to find a technition capable assessing and/or correcting the system if necessary. It may be that this system was not designed well or has degraded with age. I know the previous owner had the compressor changed.

I do not know much else about the history of the system, but if it is only as good as resistance heat I would pick that because it is quieter. Other more modern systems advertise cost savings, but at the moment I don't see them.

Thanks,
Tom

 

[TomHussey]

I should have added this link to my previous post. This is the accumulator with the heat exchanger built in...

http://www.refresearch.com/Portals/26/PDF/5.pdf

Is this sort of set up common in industry or other refrigeration equipment? I know that the intent is to prevent liquid from returning in the low side. I believe it increases the level of "super heat" to ensure this .(?)

I notice that this unit (HX3738)is suggested for systems up to 4 ton when used with R22 and an evap temperature of 4C. In my case I think the evaporator is even a bit colder as I see ice on the lines where they enter the accumulator. I have no description as to the capability of the system but believed it to be 8 tom. Is there a way to determine the unit capability? If the unit is 8 ton and the accumulator is the one described will this possibly lead to compressor failure (from liquid reaching the comp)?

Looks like I need to find some good help tomorrow. The fix/replace decision is never easy with all the facts in question. I appreciate all the good help you folks have given me.

Tom

 

[ccjersey]

Any refrigeration system with capillary tube refrigerant control is sensitive to refrigerant fill level.

I would guess it is overcharged.

This is just because the tendency of service technicians who don't know what needs doing is to add refrigerant to see if that improves performance. Once it is in there, it involves getting out a reclaimer unit to remove it, so that might not get done.

The next guy comes along to work on the unit that's not performing well and tries a little bit more refrigerant to see if that helps............... etc etc.

Another possibilty is that the water side of the heat exchanger surface is fouled so that heat exchange is limited. The pump or source of flow might also be diminished.

Could also have a dirty coil on the indoor/air side, but the whole system is running so cool it doesn't trip out on a safety.

 

[AbbyNormal]

Is it an old Cantherm?


The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install

 

[TomHussey]

Thanks for all the feedback!

The equipment was built in New Brunswick by a company named "All Tech" The name plate is Aqua Tec II. All information about the unit would be appreciated, but I have not been able to find any.

In earlier posts I suggested the unit might not be making much of a contribution. I need to re-check some of the measurements from what I have now found. I see a throughput of 10 liters of water/minute. The delta temperature is 4.5C.

Now I hope this all is done correctly... taking the specific heat of water, the mass, and the delta T, I come up with about 0.7KWH recovered.

 

[BM4BRANES]

A qualified company/ tech should have no problem sizing up your situation, if or what problems exist and what your options are.It's a little rare to find compressors above 5 tons on single phase power. I do find the efficiency comment interesting. Ground source Heatpumps are widely accepted as having high co-effiency ratings, more(stable) than the 3-5 of air source. BTW,a turd over 10 years old is probably not worth polishing due to lifecycle and fouling issues.