Comments on: TROUBLESHOOTING HEAT PUMP SYSTEMS…INDOOR / OUTDOOR TEMPS VS SUPERHEAT W/ FIXED ORIFICE SYSTEMS

By: wayneshirley

wayneshirley — Thu, 11 Jun 2009 21:31:55 +0000

I have one customer who had two WSHP’s, now only one. I approached them same as air-to-air. Most of the problems he had were water related. He finally learned to check the water source before calling me. His were simple open-loop (I guess you call it that) pumping creek water. Closed loop stuff is something I’ve haven’t gotten into…nobody around here will pay the cost for a state of the art geothermal system, and don’t really need it that much…

By: Tom

Tom — Thu, 11 Jun 2009 14:32:24 +0000

Thanks again,did alot of air to air units. Wshp is new to me I understand the theory of them they are fixed orifice system 12,000 btu up to 5 tons any more info would be great.

By: wayneshirley

wayneshirley — Wed, 10 Jun 2009 00:25:03 +0000

Tom, generally speaking fixed orifice systems are charged by superheat, TXV systems by subcooling. I’m assuming your system is fixed orifice. Attempting to charge by subcooling would probably be a mistake, as it is probably fluctuating also. If the water temps are fluctuating, head pressure will vary, causing suction and superheat to also vary. The same thing happens with air-to-air systems when the OD temp goes from 75 to 95…

Fluctuating superheats, or superheats following indoor and outdoor temp changes, is the downside of fixed orifice metering devices.

By: Tom

Tom — Tue, 09 Jun 2009 17:38:50 +0000

Thank You for the info, with 275 heat pumps the water coil temp changes alot and hard to get a stable super heat should I look at subcooling instead

By: wayneshirley

wayneshirley — Tue, 09 Jun 2009 00:57:23 +0000

..the smart-a$$ed answer is probably, the easiest place to get the thermocouple connected…if we get picky, there are two superheat values: evaporator superheat and compressor superheat. Compressor mfg’s worry about compressor superheat and like to see some minimum value, say 20 degrees (F) at the compressor inlet. Evaporator superheat would be measured at the evaporator outlet, obviously. With “air-to-air” systems and air handlers in attics with long line-sets, there could be an obvious difference between the two values. In the real world with air-to-air split systems, techs will usually measure it at the service valves (with a heat pump system in “cool”). Some mfg’s will specify where to measure the tubing temperature for the design superheat value, which is usually close to the service valves.

If your water source heat pump is the “package” design (the only kind I’ve seen) the distance between the evaporator outlet and compressor inlet isn’t much, so I wouldn’t think the superheat value would vary a lot between the two locations. But to be on the safe side, closer to the compressor, the better…

By: Tom

Tom — Mon, 08 Jun 2009 19:53:20 +0000

where is the best place to check superheat on a WSHP at the Evap or near the comp.

By: Joe Marchione

Joe Marchione — Sat, 25 Oct 2008 02:54:46 +0000

Wayne,

Thanks for your great explanation. I will look into it this weekend.

By: wayneshirley

wayneshirley — Fri, 24 Oct 2008 14:13:29 +0000

I’m not at all familiar with Lennox equipment, but defrost controls come in two flavors, time/temperature and demand. Time/temp controls have selectable defrost initiate times, usually in the 30,60,90 minute time ranges. The disadvantage of time/temp controls is the fact they will initiate defrost cycles unnecessarily, which is of course a waste of energy…which is also probably the reason someone invented the demand defrost method. Demand controls compare outdoor air temperature to outdoor coil temperature and use some minimum temperature differential as the controlling factor for initiating a defrost cycle, pretty much eliminating unnecessary defrost cycles. With the increased focus on system efficiencies, demand controls have become the popular choice of many equipment manufacturers.

If I had to guess, I’d say your Lennox has a demand type defrost control, which has no options for changing the defrost cycle frequency. You can differentiate between the two systems in a couple of ways. Time/temp controls have a single temperature sensor that attaches to the outdoor tubing somewhere, and the control board has the 30-60-90 values printed on it. The demand controls have two sensors, one is attached to the tubing, the other exposed to the condenser inlet air flow…and there’s another post somewhere on this blog relative to defrost controls you might look at.

By: Joe Marchione

Joe Marchione — Fri, 24 Oct 2008 05:13:08 +0000

Wayne,

Thanks for sharing your knowledge. I have a few questions if you don’t mind, is there any way to change the balance point or the defrost time on a Lennox heat pump? It seems that if I set the balance point lower and had it defrost more often, then I would be able to get it to work below the 40 degrees F that it seems to be set to now.

Thank you in advance for your answer and have a great day.

By: wallace

wallace — Wed, 03 Sep 2008 08:43:15 +0000

Paul, how you’re doing. you over charged the unit. It seem loke you charged the unit too quickly with liquid. You must place a little juice, gas to keep from taking oils with freons throughg the unit. took a chance of lock rotor. On a home unit, you always bring suction pressures up around 45 degrees. anything over that; your superheat rangfe starts toget wider.
Sit at the location and check the low gauge, if it starts to drop crack in two ounces at a time until the gauge seem steady. Take of the gauge and go make some money would the unit pulls down for a few hours or over night when possible. When you go back the next day; add freon till you reach the the 45 degree magic number. Now, some squol units magic number is 38 degrees and you will know by looking at the high side reading. they run close to 300 to 350. Take care yourself; I hope I helped a little. Practice more super heat, it’sood for us. have a great day.