mini-split compressor installation: mineshaft?

[daxo]

hi
this is NOT a DIY question, i am trying to get a reality check on a contractor who insists he cannot do an install the way i would like to do it.
i have 2 specific questions but first let me describe the situation. i have a cottage in upstate new york (long cold winters and usually a fair amount of snow). about 30 feet away is the mouth of an old mineshaft (it goes horizontally into the side of the hill). inside the mine its about 50 degrees year round. this seems like an ideal spot for an air source heat pump. (see also hvac-talk.com/vbb/showthread.php?t=164426) specifically i am considering a fujitsu mini-split.
just because the mineshaft is near to the cottage doesnt mean its an easy reach, and i think my contractor is inventing reasons because he just doesnt want to do it. i cant blame him in a way, but i am paying. "the customer is always right" and i am here in this forum to do my due diligence and make sure my idea is, in fact, right.

the contractor says running the refridgerant lines that far from the house would subject them to failure due to freezing, that they are uninsulated and so any efficiency gains by placing the compressor in the mine would be offset by the temp loss in such a run, etc. yet an architect friend (who admits he is no engineer) regularly sees compressors installed at great distances from houses. the fujitsu spec sheet says max run of 60 feet with a max vertical gain of 40 ft. my placement is within those figures.

my questions: can mini-split linesets be run 60' outdoors? what if any additional insulation is needed? what addtional issues might be involved?

second: am i crazy to pursue this idea? the mine is much larger than than the basement volume mentioned in the thread referenced above, but even if the compressor did suck all the heat out of the mine i wouldnt be any worse off than if the compressor was outside at the back of the house (where it will be inaccessible to have snow removed from the unit during the winter) , right?

i am happy to clarify any part of this situation. i am hoping especially to hear from professionals who have run minisplit/heat pump linesets in exterior conditions.

thank you so much for your time.

-dave

[TwincamDave]

I sell mini-splits and if your total length is what you say it is, mechanically it should be ok. Realistically not sure how much heat you will get(it's pretty long outside). On a mini-split your lineset is your metering device so heating could be challenging and you will be waisting heat on the long run. I can see your contractors hessitation.

[beshvac]

both the line sets on a mini split have to be insulated , this insulation can be increased to help off set the heat loss/gain over its length say from 1/2 in to 3/4in , are you going to trench for the line set , the insulation will not stand up to the wear and tear on outdoor nature , animals , vegatation, solar , etc , in theory can be done , but it would be an unusual type instalation so many ifs and buts , you may have to pay time and materals and look for an adventous contractor ,

Yeah, the ones 6 months from now when you call "sorry this number has been disconnected" I like your current contractor, he's doesn't sound like one that wants to take responsibility for the install as apposed to "write the check, I'll do it anyway you want"

Buried linesets or worse yet exposed linesets running along the ground are not the best places to put them.

[woody19]

I have seen linesets installed inside pvc pipe and run underground without any issues so it may be a consideration.

[beshvac]

I have seen linesets installed inside pvc pipe and run underground without any issues so it may be a consideration.

Where at? This guy is next to a mineshaft....rocky ground?....gonna be buried under snow for 30ft? The guy that looked at the job doesn't want to do it....he doesn't want the money? or the responsibility for a bad idea?

[beenthere]

You said the mouth of the min shaft is 30 foot away. You would probably need to have the mini 20 to 30 foot inside the shaft to be of any use. That would probably put you over allowable line set length.

PS: Do you own the mine?

[woody19]

Where at? This guy is next to a mineshaft....rocky ground?....gonna be buried under snow for 30ft? The guy that looked at the job doesn't want to do it....he doesn't want the money? or the responsibility for a bad idea?

So what's your point?

[beshvac]

So what's your point?

point is we are outside normal. burying linesets for that length isn't a good idea and trying to leave them exposed in the snow isn't a good idea either.

[kangaroogod]

Do you own the property where the mineshaft is located? It is an interesting concept. My first though was also to bury the line set and sleeve in PVC. The cold conditions should not effect them. After all they are designed to be exposed outside. I am not sure what area of upstate ny you are located. Feel free to contact me if you would like. My information is in my profile. I enjoy unique opportunities.

[daxo]

hi thanks for the very many replies!

i do own the mine. very astute to recognise that yes it is very rocky ground, and a fairly steep hillside to boot so that digging a trench (presumable below frost level) would be quite an undertaking. the mine shaft is not very long, perhaps 100 feet, but there is a nearly constant pressure of air being blown outward so i assume the condenser placement i selected would be fine and the measurement to that point was within the allowed lineset limit.

my contractor is very perfectionistic and conservative (these are very good things!) but he is more a plumber and solar hw installer than an hvac guy. his objections were rather vague, to my thinking. my area of expertise is huge temporary electrical distribution runs, and i am more inclined to "think outside the box". i also know that sound decisions are made by having enough information and if you have good technjcians then the fatal errors happen in the planning stage. i really appreciate the members of this forum sharing their expertise.

as i get more insight i can be perhaps more specific with my questions: if the lineset has to be in a trench then the idea is a dead end. but if the linesets are designed for exterior use and we will already be running about 20ft outside, then why not another 20 feet in insulated pvc which is enough to get into the mine opening (and another 20 ft to the spot inside where it would sit)? the consensus seems to be mostly against it but i am not entirely clear why.

i understand the temperature difference (between ambient and refridgerant) are much greater in heating than in cooling mode, thus more loss. but it seems it would be more than offset by the heat pump working at nearly optimal temp 24/7 rather than struggling at the edge of its capability in sub-freezing ambient outside with a huge drop reduction in efficiency.

the mini-split would be the primary heat for the cottage, which is a rented to a paying tenant, and i am dubious of them (my own conservatism) and whether they will be able to extract enough heat from a new york state winter.

lastly, it seems retarded to keep throwing money at fossil fuels when i have this resource of ground temp air so close at hand. i dont have any figures on how much air a heat pump would use to draw heat from, perhaps i am being retarded in thinking this would work at all. i am willing to accept that conclusion.

thanks again for you patience with me an my (crackpot? or not?) questions.

[kangaroogod]

Your electrical will need to be buried at a depth of at least 18" in conduit per nfpa70. Sounds like that was the deal killer