piping insulation in the outside unit

shamus47

The manufacturer (trane) for my heat pump does not insulate the copper piping inside the outside unit. This includes the hot gas discharge line from the compressor the reversing valve and all of the associated tubing leading to the service valve. The line from the service valve is insulated going to the indoor unit. MY question is, is there any downside to insulating the exposed tubing. In total it is probably only about 2 feet all together but why would you expose this to the winter temps in the northeast?

Empire_2

Basically it's a non factor and probably impractical.

shamus47

I may be straying into crackpot territory, but the way I'm looking at this is if you had a boiler and it was outside and was pumping hot water into a coil in an indoor blower wouldn't you insulate the pump and the piping? In the heat pumps case , the hot gas discharge pipe along with the muffler, the reversing valve and the piping leading to the service valve are all uninsulated and sitting in below freezing temps at the hottest point in the cycle. Yet every installation manual says to insulate the line going into the building but makes no comment about the uninsulated portion in the outside unit. I'm no thermodynamics expert but I have to believe you are losing considerable btu's to the outside conditions.

JUGHNE

For heat pump operation I think of the hot gas line as feeding the condenser coil inside the house AH. The coil extracts the latent btu's thru phase change of HG to liquid. (Not unlike a steam radiator). The condensed liquid than returns to the outside evap coil and is exposed to the "warmth" of outdoor ambient temps. and boils back to gas then to comp. (steam boiler turning liquid into gas/vapor).

The hot gas line from compressor to reversing valve needs to lose heat in the summer AC mode, insulating that could overheat oil/valves/etc??? I don't know.

The large suction that is insulated to your unit could maybe be insulated all the way to the reversing valve.

If the manufacture could squeeze more SEER & EER out of equipment with line insulation alone, I'm thinking they would want higher R value insulation on Hot gas lines going into the house. (That would not add any cost to their product and make their ratings shine more.....the expense would be on homeowner/installer.)

IMHO the heat loss must be minimal as the real btu exchange takes place in the inside condenser.

shamus47

The hot gas line is 1/2" copper and the muffler is about the size of a typical liquid line drier. I agree that you wouldn't want that insulated in the summer. I'm in northeastern Pa and the temps are consistently below freezing in the winter.

Empire_2

Discharge line in side the condensing unit does not give up any latent or sensible heat as it is still hot gas. most, not all is heat of compression. The coil does the actual work. so long as your inter connecting lines are insulated, that is the real concern. Even the suction line is so short that you would not pick up any additional S/H going into the compressor. If you were to plot it on a P/E chart, the graph would not change from overall system performance. Now if the compressor was remote and traveling some distance to the condenser, you bet the line should be insulated but mostly for keeping any condensing going on before it got to the condenser.


Peace;
Mike T.

shamus47

Thanks for replying, I get that the change of state is where the bulk of the work is done but the hot gas is being discharged in the outside unit thru the discharge pipe and the muffler and the reversing valve and on thru the service valve with no insulation and the fan running and outside temps in the 20's. I don't know how this isn't starting the condensing process prior to it getting to the indoor unit where theoretically you would want to remove as much heat as you could so it would blow into the living space. As I said earlier, I could be just barking at the moon but I just can't get why you would want to cool this gas down in the outside unit.

Empire_2

OK here is a neat little test just to (if anything prove my point) address your concerns. During winter operation and choose the day of your choice, strap on an accurate temp probe to the discharge just out of the compressor and the other just before it leaves the condenser on the way to the indoor coil. I know it is summer.........:-) I think this will put your concerns to rest. Let me know if there is actually any temp diff. If it were more than 1/2 * I would be amazed. If it were more than 2+ * before it hit the indoor coil, I would be equally be amazed. Like any measurement in ref. 5 min run time will allow the system to reach it optimum performance curve..

Peace;
Mike T.

JUGHNE

Again my point that if it made a major difference the equipment people would have done it already and required superinsulation on the hot gas line, (not at their expense BTW)/

They scratch to gain a half point SEER with time delay off control on indoor fan. (used to anyway).

shamus47

Thanks for the posts. The idea for the differential temp probes is a good plan. First really cold day I'm going to try it. In reality even if it proved efficient to insulate for winter I could see how you might have to remove it for summer ( on this unit you have to pull the top discharge fan to get at the piping and really bend to reach the muffler,ugh). Still why all the equipment manufacturer's emphasis on insulating the exposed gas line outside the unit and in the crawl space if they are not worried about heat loss? The exposed piping in this unit is 1/2" copper about 2 feet to the reversing valve and about another foot of 3/4 copper from the rv to the inside port of the service valve. You guys are probably right it is probably not worth the trouble still it is counterintuitive to expose hot to cold and with all the product recalls my faith in manufacturing excellence is a little shaky. Once I have the temp readings I'll post the results.

JUGHNE

The emphasis on large line insulation is to prevent condensation sweating during AC usage, causing building damage. Also assist in compressor cooling.

Heat pumps have be in mass production for 50+ years, again if it made a difference in efficiency there would be more insulation required.

We await the results of your experiment, thanks.

Bob Bona_4

Imagine the mess after a few years of exposed armaflex in an open cabinet. Or the logistics of every unit getting that treatment. It is what it is.