Trane Heatpump

[marca]

1. I had 2 Trane heat pumps (installed May 2002), model TWY036B100A1 (3 ton) and they are coupled with the Trane variable speed air handler and matching coil, model TWE037E13FB. I believe that the heat pump has a scroll compressor. Is it best to protect this type of scroll compressor during brownout periods (when the power goes off for a second or two during a storm) while the unit is operating? I always thought that it is best to wait 5 minutes prior to restarting compressor in order to provide time for pressure equalization; otherwise, the compressor will experience harmful and undue strain. I do not know if my units have "anti short cycle" circuitry built-in. I have read about installing this type of 5 minute time delay relay in the condenser unit between the 24v thermostat wire and contactor. I believe that what I may need is called a "delay on make timer". I also have read that some thermostats have this type of circuitry built-in to the thermostat thus making it unnecessary to wire inside the outside condenser unit. I have only a basic Trane Weathertron thermostat (BAYSTAT 240A) manual 2 stage heat, 1 stage with cool mercury bulbs.

2. Also, is a "hard start kit" recommended for my unit? Will a hard start kit do anything to prolong the life cycle of my equipment?

3. Also, during installation, no filter/dryers were installed. One of the old units had a grounded compressor (burnout?) and the lineset was not changed due to thru-the-wall/ceiling considerations. I do not know if the installer blew out the lines with nitrogen followed by vacuum. Is it true that in my units, Trane already put filter/dryers on both the suction line and the liquid line thus making additional "aftermarket" filters unnecessary?

4. During cold weather, when the temperature goes below 20F, I manually switch over the thermostat to emergency heat. After all, at that low outside temperature, the heat pumps are not putting out that much heat, and I may as well "save" the pumps from excessive run time. What is the device called that I can install outside that can be set to shut off the heat pump when the outside temperature reaches a certain temperature? That way, I won't have to bother to manually switch it off at the thermostat.

All comments and suggestions welcome. Thank you very much for your time and consideration.

[BaldLoonie]

That is a scroll compressor. Supposedly they can start quickly after shutting down although with the non-bleed TXV on the high SEER system that could be a challenge. That unit does have a full start kit according to the Trane parts program.

Trane includes a tiny liquid line drier in the unit. They recommend against external driers. What should have been done is a suction drier put in upon startup (in cooling mode only) and removed after a week or 2.

Turning a high SEER scroll unit with demand defrost off in the 20 degree range is costing you money. If anything, run it down into the single digits before shutting off. An outdoor stat can do that automatically.

[mark beiser]

If you insist on changing over to emergency heat below a certain outdoor temperature, wich would be only for comfort, since it costs more money to operate it like that, I would recommend a Honeywell Vision Pro thermostat with an outdoor temperature sensor.

The Vision Pro with outdoor temperature sensor will not only display the outdoor temperature for you, but it can be set to lock out the heat pump automatically when it is below the temperature you select. You can also set it to lock out the auxiliary heat when it is above a certain temperature.

[mfb]

Mark

I'm confused. I would think that at some point the outside tempature drops so low that it costs more to run the compressor than the heat you'll get out. Thats where the compressor cutoff comes in. I'm not sure exactly where that point is, but you seem to be saying that there is no brake even point. How can this be?

Could you please explain.

[marca]

mfb-- I wholly agree! Based on my personal experience, there is a point of "diminishing returns" when running the heat pump in very cold weather as contrasted to shutting it down and activating the resistance heat. I do not know what that low outside temperature is, however, it is also dependent upon outdoor humidity, wind, sun/shade, etc. around the condensing unit.

For instance -- At outdoor 20F, my plenum temperature is 80F with only heat pump running. At this temperature, when the thermostat calls for heat, the heat pump runs for a long time (sometimes 1 hour) to satisfy the 2 or 3F shortfall. Instead of "wasting" the heat pump, I simply turn it off, activate the aux. resistance heat, and the thermostat is satisfied within 5 or 10 minutes. I guess it is only trial and error in addition to a lot of observation and recording of both plenum and outdoor temperatures that would determine efficient point in which to terminate the heat pump. I am interested in both "saving" the heat pump from unproductive/inefficient heat transfer (due to low outside temperature) and preventing a waste of electricity. Of course, I realize that resistance heat is more "expensive" than "heat pump heat", however if the heat pump just runs and runs and runs, that is a larger waste of electricity, minimal heat transfer and unnecessary wear and tear on the heat pump.

In my instance, whenever the heat pump can not produce (transfer) heat in the plenum in excess of 80F, I manually switch it over as described above. Any thoughts?

[filterchanger]

i think if the heatpump runs a full hour to satisfy a 3 degree temp and doesnt bring on the elec heat then this is the problem,, the t-stat should bring on your elec heat to help the heatpump out in run times like this,,at 20 degrees out your supply air will be more with both sources of heat on, then with just one of the 2 sources of heat

[Shophound]

I agree with filterchanger, marca. Looks to me that either your thermostat is not calling for aux heat, may not be a two stage stat, or may not be wired properly either at the stat or in the air handler.

IMO, when both stages of the thermostat are calling for heat on a heat pump system, the second stage heat should bring up the space temp rather quickly, then cycle off to allow the heat pump to finish the job.

[airconman]

I had a five ton system not come with the hard start kit. Dimmed the lights pretty good when it came on, however trane gave me one to put on it and called it warranty. Some models came out early without the start kit. USE TRANE START KIT ON IT.

[dmoneyc22]

oh my god you obviously live in the northern part of this country. most trane high eff. systems have a start assist in the control area of the unit. if you insist on using your emer.ht them you must be tryiing to keep your home comfy. not recommended. if you have a problem heating and your worried about getting cold due to a system that can't hang with the big dogs for heat invest in a gas furnace for back up.

[marca]

Filterchanger -- Yes, if both heat sources are operating simultaneously, plenum temp. will be much higher. However, if second stage kicks in, meaning that there was a 2-3F drop that called first stage on, then another 2-3F drop that called for second stage to kick on, then you are fighting a losing battle. Once the resistance heat satisfies that additional 2-3F drop, it will shut off. However, the heat pump will continue to run, and run, and, run; but it will NEVER satisfy the original 2-3F drop. Now, the cycle will continue..... another 2-3F drop, calling for second stage heat, second stage satisfies while first stage keeps running, first stage can not keep up, another 2-3F drop, second stage kicks in again, etc, etc., etc. In my opinion, it is a waste of both electricity and heat pump wear and tear to operate a system in this fashion at low temperatures. That is the reason I switch OFF the heat pump and switch ON the resistance heat during periods of low outside temperature. My logic is; if the heat pump is unable to satisfy within a reasonable period of time, then it should not be running. Makes sense?

Shophound -- According to my personal experience, once the second stage is satisfied, the heat pump can never "finish the job" within a reasonable amount of running time at such low temperatures.

Airconman -- Thanks for the info. My lights do not dim, so I assume that hard start kit was factory installed.

Dmoneyc22 -- Thanks for verifying the presence of start assist built in my units. Unfortunately, we do not have gas available. I never run the thermostst above 70F during winter.

[jeffkillen]

Big dogs also eat more!

[filterchanger]

Just about everyone on here gave you the same advice,,,and yet you still think you are right. when the heatpump can not keep up the backup elec heat should come on and stay on until desired temp is satisfied,,now if the temp drops quickly and the process starts over in say 5 minutes or so,then you have a poorly insulated house,, your system may not be installed or charged correct which may be the problem,,what you need to understand is that when a heatpump is operating correctly then it will be able to maintain a set temp once it is established at 20 degrees outside,,,if the heatpump is operating correctly do not shut it off

[filterchanger]

also you dont want a delay on make timer you need a delay on break timer,,

[jrbenny]

Originally posted by marca
In my opinion, it is a waste of both electricity and heat pump wear and tear to operate a system in this fashion at low temperatures. That is the reason I switch OFF the heat pump and switch ON the resistance heat during periods of low outside temperature. My logic is; if the heat pump is unable to satisfy within a reasonable period of time, then it should not be running. Makes sense?

It's your opinion. Just doesn't make it right nor does your logic make sense.

A heat pump provides useable heat well below 20°F, and it costs more to run strip heat only.

Sit down and do some math. You'll need the following information: BTUH capacity of your strip heat; running amps of your strip heat; running amps of your heat pump; BTUH output of your HP; KW-H cost; heat loss of your structure at 20°F.

Now see what's cheaper to run. I bet you'll find that the HP running continuously with b/u heaters bumping intermittently is significantly cheaper than only running the b/u heaters.

I've done the math. I want you to see for yourself.

[jeffkillen]

Originally posted by jrbenny

Originally posted by marca
In my opinion, it is a waste of both electricity and heat pump wear and tear to operate a system in this fashion at low temperatures. That is the reason I switch OFF the heat pump and switch ON the resistance heat during periods of low outside temperature. My logic is; if the heat pump is unable to satisfy within a reasonable period of time, then it should not be running. Makes sense?

It's your opinion. Just doesn't make it right nor does your logic make sense.

A heat pump provides useable heat well below 20°F, and it costs more to run strip heat only.

Sit down and do some math. You'll need the following information: BTUH capacity of your strip heat; running amps of your strip heat; running amps of your heat pump; BTUH output of your HP; KW-H cost; heat loss of your structure at 20°F.

Now see what's cheaper to run. I bet you'll find that the HP running continuously with b/u heaters bumping intermittently is significantly cheaper than only running the b/u heaters.

I've done the math. I want you to see for yourself.

[jeffkillen]

I agree with jrbenny,leave t-stat set and let the system do it's job.Don't over try to second guess science.

[go_redskins]

Originally posted by marca
Filterchanger -- Yes, if both heat sources are operating simultaneously, plenum temp. will be much higher. However, if second stage kicks in, meaning that there was a 2-3F drop that called first stage on, then another 2-3F drop that called for second stage to kick on, then you are fighting a losing battle. Once the resistance heat satisfies that additional 2-3F drop, it will shut off. However, the heat pump will continue to run, and run, and, run; but it will NEVER satisfy the original 2-3F drop. Now, the cycle will continue..... another 2-3F drop, calling for second stage heat, second stage satisfies while first stage keeps running, first stage can not keep up, another 2-3F drop, second stage kicks in again, etc, etc., etc. In my opinion, it is a waste of both electricity and heat pump wear and tear to operate a system in this fashion at low temperatures. That is the reason I switch OFF the heat pump and switch ON the resistance heat during periods of low outside temperature. My logic is; if the heat pump is unable to satisfy within a reasonable period of time, then it should not be running. Makes sense?

Unless there's something wrong with your heat pump, running nonstop is not a sign that it's inefficient. It's simply the result of your homes heat loss exceeding the heat output of your heat pump. And running nonstop isn't really bad for your heat pump. Someone around here even has a signature saying - "The worst thing you can do to a compressor is to start it." So given a choice between running nonstop and frequent starts and stops, nonstop is preferrable.

From a strictly efficiency point of view, you'll probably find that the heat pump is more efficient than resistance heating even at 0°F. Here's my computation for how much more efficient the heat pump is compared to resistance heating. The numbers below are based on my setup which is a Goodman CPLT48 heat pump with a Goodman AEPT60 air handler which has a 10kw heating coil.

Looking at the manufacturer specs on my heat pump/air handler combination, I can see that at 0°F, it can generate about 25K BTU/H at a COP of about 2.2. So even at 0°F, it's generating 2.2x as much heat as it is consuming in electricity. But we need to take into account the loss due to the heat pump's defrost cycle.

My heat pump is setup to defrost every 90 minutes. At 0°F, it will probably defrost for a full 10 minutes each time it enters the defrost cycle. So a complete heat/defrost cycles is 100 minutes long. Now let's calculate how much total heat is generated and how much electricity is consumed.

For the 90 minutes that the heat pump is heating at 25K BTU/H, it generates a total of 37.5K BTU's (since 90 minutes is 1.5 hours). The electricity it consumes during the 90 minutes is 37.5K BTU / 3.412K BTU/KWH / 2.2 = 5.0 KWH.

During the 10 minutes that the heat pump is defrosting, the heat pump is removing heat from the house at a rate of about 48K BTU/H offset by the 34K BTU/H generated by the 10KW heat strip in the air handler. The net loss of heat from the house during the 10 minutes is 14K BTU/H * 1/6 hour = 2.3K BTU's. The electricity consumed during the 10 minute defrost is about 0.6KWH for the heat pump and 1.7KWH for the 10KW heat strip (10KW * 1/6hour).

So during the 100 minute heat/defrost cycle at 0°F, the net heat output is 35.2K BTU (37.5K-2.3K). The electic usage is 7.3KWH (5.0+0.6+1.7).

Had you used resistance heating, 7.3KWH would have generated 24.9 KWH (7.3*3.412). So the heat pump is still 41% more efficient than resistance heating even at 0°F (for my setup). Do you own math and make your decision.

[marca]

Thank you all for your replies! Regarding my Trane 3 ton heatpump model TWY036B100A1, could you please let me know if this unit was manufactured with an anti-short cycling timer installed in the unit? If not, I thought it a good idea to install the delay on break timer with brownout protection. Any thoughts or recommendations regarding timer model? Also, if I perform the install myself (it is simple and straightforward), will this effect my 10 year Trane warranty? Thanks bunches.