Im in the cincinnati ohio area and am looking to replace my system with a Geothermal Heat Pump.  I have quotes to put in a 3 ton waterfurnace 038 envision I think it was with the desuperheater and 15 kw backup.  They want to lay a horizontal loop field of 350 feet in length at a depth of 6 feet and put  three 3/4 inch pipes going out at bottom of 36 inch trench,  backfill 1 foot of dirt over top and return three 3/4 inch pipes back to manifold for the closed loop.  I made it clear that I dont want to be short looped and was promised that this was plenty of loop for my system.  I have a well insulated and efficient 1 story brick ranch thats 1850 sq feet on top and 1000 sq feet in finished basement underground.

I was told the basement really doesnt add any load for the need of a 4 ton system and he felt that I would be fine with 3 tons. Three is what I currently have in a heatpump.  He also said the ductwork would be close on supplying cold air return to the system if it were 4 ton and also the eer actually went down in the first stage with a 4 ton over the 3 ton waterfurnace. 

Im thinking he sounds good and he comes highly recommended and I have talked to several people whom he installed similar systems to their house and are very satified.

I still dont know if the loop sounds right

Would it pay to say add enough loop for a 4 ton system but run a 3 ton heatpump,  Is that even worth it if im only going down 6 feet and returning 5 feet deep?

Suggestions and comment much needed..

Also what is the opinion of adding a trane electronic air clearner to the tune of 910 bucks.  we dont have allergies other than slight seasonal issues and usually have the house windows open on nice spring/fall days....would we even know the difference of and electronic air filter when the filter on the waterfurnace is so highly rated?



Thanks  
Tim in Cinci

Hi Tim,

I can't say if the loop is long enough. Ask the bidder to give you a written guarantee with penalties that the loop will not drop below 32°. There are contractors out there who do this.

Then you will know how confident he is in his loop design.

We would tend to go 450' of 6 pipe trench in mid MI, so given how far south you are (compared to me) I can't knock the design. I know we over kill at 150'/ton but there are lots of factors.
What jumps out at me is that the aux coil has more heating btu's than the heat pump.
J

I'm in northern Indiana and we put in the same system you are looking at last March. The loop installer put in the same kind of loop that your installer is talking about. Initially they were only going to go with a 300' trench. I convinced them to go another 50'. The installer advised that they go with 100' per ton with a six pipe trench. My EWT is down to 29. I was hoping it wouldn't go that low. My system is still maintaining temperature but I do have long run times.

Given the extreme cold weather a 29* EWT isn't indicative of poor design. There is usually a pretty fair weather difference between northern Indiana and Cinci. Let's not forget we put antifreeze in these for a reason. Many systems are designed to operate at as low as 10 or 15 degrees, so it is clear that 30 plus temps (while cheaper to operate at) are not necessary.
I think it is fine to ask the installing contractor if you can purchase extra feet of loop to raise operating temp (and lower operating costs). But bear in mind that most contractors oversize to begin with (extra pipe is cheaper than not enough) and that antifreeze and larger flow centers may cost more than savings.
I also think that at some point, if you've done your homework on the contractor, spoken with his references, had your questions answered satisfactorily and have the appropriate written guarantees then you should let him do the work you're paying for and trust your research. My customers are usually offered different choices, but at the end of the day the design must be mine if I'm to warranty performance.
I'm still curious about the aux coil size by the way, have you asked for explanation on that?
J

I'm a bit curious about aux coil sizing - given that strips are cheap, and assuming electric service spare capacity is available, why not size aux to meet total load in case of failure of compressor, contactor, loop pump, reversing valve, etc?

Down here loss of heat (or AC) is a serious inconvenience, but our pipes or people won't freeze because of it.

In this case if Man J supports an 038 geo, then what you are getting at is that 10kw should suffice?

I'm not sure I buy that basement adds no appreciable load - if both slab and foundation walls are quite well insulated then maybe so, but if not, then how would the basement be kept above earth temp all winter without some heat?

The unfortunate part of the extra coil capacity is 25 amps. Depending on electric service to house that can be significant. Particullarly if upsizing wire to home is required to carry extra load, that can be awfully expensive. If load is a non-issue then I agree it doesn't matter, I'm simply curious.
J

Perhaps we have the same lurking suspicion that the designer here is a bit unsure about geo, so is piling on the strips just in case.

Another subtle objection to strips is the permanent air flow restriction they create - 0.10" wc or so. Modern ECMs overcome that by spooling up a bit, but it adds a bit to running wattage to make the set CFM. Not much, but it adds up, particularly in constant fan apps.

I don't know but suspect that excessive strips would increase ESP.

What are your thoughts on "basement doesn't increase load"? We don't have many here.

I could say that basements don't add much to the load.

I went back and looked at the heat load I did on a 3 story house ( basement + two floors).  Each floor being about the same size.

The total head load was 35,000 btuh  and the basement portion was 7500 btuh or about 21%. 

If they closed off the registers to the basement,  ( like I do ),  then the load would be even less.

My experience is the same as Dewayne's in that basements add a fairly small load/sf. Curiously close to the load of un insulated duct in un conditioned space. I always factor them in because of the similarity in loss.
J

Why wouldn't the basement counted as no load? If it's finished, it must be heated space right? It must add some load, perhaps not enough to push it into a bigger system, but it has some impact.

I have just been told by one installer that my load for the first floor, 1260 sq, will be 28,500 Btuh and the same for the second floor for a total of 57,000 Btuh, according to his manual J study. No mention of the same sized full basement. Does this sound right? Seems a lot to me. The house has the identical size rooms and layout upstairs and down with no extra high ceilings. Looks like he's calling for two three ton systems, one up one down.

What size loops would I need. The soil structure here is loam over sand with some layers of clay. Our climate is milder than New England's, but colder than Pennsylvania's.

I wish this were simple.

if you have a present furnace keep it for backup and dont use the strips you can do that. if you have no algeries pass on the filter it just runs your cost up thats an optional thing. the basement has to be counted in your load. when i dont burn wood you cant stad it down in my basement yours wont be any different. wonder what sort of price he is giving you? a newbie learning very fast.

bob

Sunny, this doesn't pass the smell test. There is no way that the main floor and second floor of a two story house should have the same heat load. The second floor has the heat loss of the ceiling while the first floor has no heat loss through the ceiling. Be very careful about the guy who gave you this line!

I'm with Dewayne...also curious why the load indicated two 3 ton units to this installer, i'd've guessed 4 tons total based on load.
j

Dewayne hit the nail on the head on this one. No way does it have the same load.

Sunny..

go to this site and spend $49 for a heat load progam. 

Then  you  can do your own.  Then you will know who is giving you the BS.  Once you have the heat load,  then we can help you with how many feet of pipe you need.

Let's see. Heat rises so heat is going up from the first floor to the second floor. The basement will provide fairly good insulation for the ground level floor. Nope, that load calculation makes no sense.

Since this is a replacement, the obvious question is, how well does the existing 3 ton air source heat pump heat the house?  In theory you should not need a larger water source unit than air source unit.  The theory is that the ground is warmer in the winter and cooler in the summer than outside air.  This is part of the reduced heating cost theory.

Slightly over sizing your loop is only going to increase the installation costs - it will not harm  your system and may help.  Keep in mind that a proper design maintains the design temp about 99% of the time.  So on those two or three coldest nights of the year the unit might not maintain full design temp for a few hours.   Designing this way saves you money.  And a strip heat back up should handle those two extremely cold nights....