Hi all, I'm hoping I can get some assistance on a consensus for the geo system I want to install in my soon-to-be built house. Basics now, more details if necessary (or by request.) Building a 2450 sq.ft. single story house in Michigan (SE-ish). It will be 2x6 exterior wall with 1" spray foam, Superior Walls basement, 8 ft. doors, 9 and 10 ft. ceilings, primary windows facing SW. Up here, heating is certainly higher priority than cooling, but humidity levels are high in summer. I received four different quotes and they are quite a bit different from each other. They range from 3 to 6 tons, some with an HRV, some without. All used the manual J heat load calculation. Obviously all four cannot be correct. How do I determine which of the quotes is (the most) accurate? One person said they recommend the 6 ton system to keep operating costs down. This makes sense to a point, but will a larger system compromise the ability to adequately dehumidify in the summer? I really don't understand how they came up with different system size quotes given they were all working off the same exact data. I want to do this right the first time and I simply don't have the expertise in geo systems to understand why I have different quotes, or to determine which is the most accurate. I need help, please! p.s. One of my quotes came from someone who posts here. That person may want to keep our relationship confidential for now so as to keep replies "untainted," but it's up to that person.

Can't blame you for wanting to do it right the first time. Has anyone offered you a written performance/comfort guarantee, like Doc offers to his customers? I don't remember the details, but I thought it was impressive when he explained it. Check all references and ask them questions about sizing as related to their comfort, utility bills, humidity, etc.

One of the contractors offered a comfort guarantee. It happens to come from the most expensive quote.

I did send all four the same set of questions, but they may not have been the right questions to ask. The answers I received from everyone were not quite what I was looking for. The sad thing is that those who provided operating costs for their system, they were all negligibly different. How can a 4 ton system cost the same to run as a 6 ton system??

I know that desiring a geo system puts me amongst the "cutting edge" in HVAC installation (as compared with existing more common technologies), but it seems that obtaining accurate and reliable comparative information on geo systems can make one a little bloodied... if we already had the gas line installed, I would likely go with gas forced air instead of potentially making a bad decision on a geo system at this point. The comfort guarantee is a nice piece of mind, but is it really worth an 11% upcharge over the *average* cost of these four quotes? (it's more than 20% upcharge from the cheapest system)

I meant asking the references the questions.

Are the manual J results similar, and the installers are suggesting different equipment sizes, or are the manual J results very different?  We had one manual J calculation that was just plain wrong, the other 4 were in the same ballpark.

I wonder if it might be worth trying to calculate the manual J yourself. There is at least one program that people here have mentioned with a temporary software license. Others here can give you more information on this if you are interested, and they can probably give you feedback on how easy/difficult the program was to use.

South eastish Michigan???? hmmmmm who could that be???
That was to easy it's Joe.
Joe has a long record of good installs, calls a spade a spade, and has made public the lengths he will go to to make it right the first time. He also has a reputation for spot on loads with no fluff in the design or cost. If it were me my search would be over in your locale.

P.S. I am not a paid spokes model, just a big fan
Joe,
thanks for the inquiry about me commuting to Michigan, but i am afraid that is a commitment not a commute.
Eric

Oh... did he include a buffer tank in his quote?  Just kidding. 

I'm pretty sure Joe would be happy to spend some time with you to make you more comfortable with his calculations.  Of course, time is money.  Just trying to help.

Aw man, Eric! now you've let Joe out of the bag...

It's not that I don't trust Joe, its that I don't trust *any* of them! (No offense Joe.) I feel like a blind man who just found a stray dog and I've got four different vets telling me the dog is four different breeds - I have no way of knowing who is correct.

I only received the calculations from one place, who proposed a 6 ton system. They are pasted below. Joe installed my brother's geo system and they are very happy with it (but they've had it less than 6 months), and it was a retro in a completely dissimilar house style. My builder has worked with someone whom he trusts, but I have no experience with that installer. From my research, the 6 ton systems sounded much too large, but without access to the man J calculations, I am at a loss. It simply baffles this engineer's mind how the same source data, run through the (supposedly) same load calc, can result in three different results. As I said at the beginning, they all can't be right. That's really why I'm here and that's also why I didn't mention Joe in the beginning - I don't want his rep here to influence any third party recommendations/opinions.

That being said, here are the results (partial) that I received from one vendor:

System Design Data
Design Data: Comfort Conditions:
Heating Load: 79,174 Btuh Heating Setpoint: 70 °F
Heating Temp Diff: 68.0 °F Cooling Setpoint: 75 °F
Cooling Load: 42,630 Btuh Start Cooling Temp: 75 °F
Cooling Temp Diff: 17.0 °F HW Temp Setting: 130 °F
Constant Fan: Yes HW Users: 4 people
Design City: DETROIT, MI Annual Load:
Winter Design: 6 °F Heating: 126.5 million Btu
Summer Design: 91 °F Cooling: 25.2 million Btu
Bldg Bal Temp: 57.2 °F Hot Water: 21.3 million Btu
Internal Gains: 14,917 Btuh HW Use - Daily: 70.0 gallons

I did specifically ask for the set points to be changed to 72/78, as that is what we typically keep our thermostat at. All said the difference was negligible.

I am confused. I don't know of any new homes with proper sealing/insulation 2400 sq ft. that should have more than 50KBtu/hr of heat loss. 79K seems really high but I will not second guess because there are a lot of parameters. I am just saying that a 3400 sq ft. home should be able to be heated with less BTUs. Something is not right. I have an old (25yr) home with 4000 sq ft. and 76KBtu of heat loss, verified by blower door and Manual J. Both correlate. This home is not tight by any means. 2x6 with poor insulation and sealing.

6 tons on 2450 SF of code plus new construction sounds about right...for points north of the Arctic Circle.

Either there is an acre and a half of windows or something else is way wrong with the load calc calling for 6 tons. Consider paying $50 for a 60 day license to use HVAC-Calc and doing your own.

I'll bet Joe came in at 3 tons with an HRV and the admonition that yes, sometimes aux strips will operate on cold nights.That's OK - spending an extra $10-20k+ upfront to save $100 in annual operating cost is a ridiculous economy, and ignores other aspects of cramming a six ton system and its gargantuan ductwork into a 2400 SF home.

Joe and I gently disagree on a couple topics, mostly owing to trading in vastly different climates, but we are in complete agreement that the knowledge and integrity of the contractor trumps all other considerations. Avoid oversizing...some is good but more is definitely NOT always better.

tlrthnu,

I live in Michigan too. I’m between Ann Arbor and Lansing in a 20 year old, 1800 sqft house. I have had my 3-ton Manual J sized geo unit for two years. It is about one ton oversized in heating for a 70˚ setpoint. It hardly runs in the 2nd stage. 10 KW auxiliary heat is available, but it has never been needed so far. I do not have HRV. I estimated my largest monthly electricity use for heating at 930 KWH for Jan 2009. I’m not suggesting the correct system size for your house, just pointing out that Manual J’s go wrong, sometimes. An experienced installer should get it right.

How I got to know Joe:
My system overcooled my house in dehumidification mode. I have Climadry, which is rather uncommon (few installed), most installers are not accustomed to troubleshooting. My system installer and other local Climatemaster dealers did not help me. I think, because they did not have the time for or the interest in educating themselves about Climadry, concerning a case that rarely comes up.

After I posted my problem here, Joe responded, and inquired about it on another forum. He paid attention to what I needed. He researched the situation with genuine professional interest at the local distributor and further at Climatemaster headquarters. Even though my system was not his baby (installed by another dealer), Joe took responsibility to make it right. As one customer, I have complete confidence in Joe’s professional integrity and customer care, experience, and fairness.

Regards,

Masoud

It seems Joe is well liked here, that's good to know! :) He's starting to sound like Mike Holmes.

I appreciate all the replies so far. This is helping me, so please, keep it coming!
The house does have a lot of windows (see attachment), but they will be high quality, argon filled, low-e. I know the amount of windows affects the HVAC, but again I don't understand the disparity between the four quotes. I don't have the load calcs for the smaller two quotes (3&4 ton), so I don't have anything to compare at the moment.
Joe - would you be willing to send me your man J calcs?

79KBTU/H sounds an awful lot for a 2450 sqf single level new built house, even with a lot of windows, that is more than 30 btus/sqf. That would make me suspicious. Based on that load I would propose a 5 ton system. The statement from one of the installers is incorrect, a larger (6 ton) system will run less efficient if oversized.
Just by doing a rough envelop calculation using R-19 walls and R-38 roof, it looks to me (roughly) not more than 60KBTU/H. But Joe being a local would know better.

Being an engineer you know that the devil is in the details and the minutiae. For you to be tottally comfortable with your choice you are going to ave to pull at least one all nighter to get up to speed. Understanding the results of a manual j calc is not easy, understanding how to express values given real world conditions, understanding what portion of the load is being met and why, and lastly how one little wrong keystroke on the software = big trouble for either your wallet or your comfort.
I would use Joe for the baseline by which you measure all others. Have him explain his design to you and then request the same of the other bidders. Install cost vs. operating cost while utelising stage three in heating is a huge point. Builders have relationships with sub contractors that they cultivate over time. Sometimes it is hard to get in that circle because the general will trust the existing relationship without waivering whether it is founded in reality or not.
This like most things is not easy. Do the work to get involved 100% or make a decision based on trust. As has been said I would trust Joe if I lived in Michigan.
Eric

The trouble with providing Man J calcs free of charge is that an unscrupulous prospect may take one contractor's hard work and shop it out to a lazy hack.

A potentially fair solution is to pay for the calc with the understanding that the payment will be credited toward the project if the bid is accepted.

As an engineer, running your own load calc shouldn't be hard - one late night totally sober or a couple shorter evenings with a few beers ought to do it. Another benefit is that you can tweak building detail choices and watch their effect on loads and required airflows. An example of this is varying window SHGC by exposure. Windows can be ordered with a factory tint that dramatically reduces SHGC. You may want that on a west wall but not on a south wall up north.

You can also run a cost benefit analysis of sprayfoam sealing the attic, bringing the duct system into indirectly conditioned space. Sprayfoam is pricey, but so is a ton of closed loop geo capacity.

I took a very quick look at the linked JPG...going out on an unsupported, free-and-worth-every-penny internet SWAG limb, I'll 'refine' my load guesstimate to 4 tons with a conventional attic, 3 tons if sealed

Comparing Joe to Mike Holmes is not unwarranted...

In youth I may have preferred comparison to "johnny" not "mike"

Chris my calculations came in (worse case) around 60kbtu (good guess doc!) and used Lansing not Detroit as the comparison city which is closer and has a few more heating degree days. I haven't completely pinned down the results of your heat loss yet as a few parts of the plan and insulation were vague to me.
That said; a few thoughts. Even if your load were 79KBTU we'd be discussing a 4 or 5 ton not a 6 ton. 4 ton would cost about $150 year more to operate but cost $4,000 less to install while the 5 ton would cost $38 more/year than a 6 ton (all heating/cooling/hot water) to operate and at least $2,000 less to install. Cost increases do not factor extra duct requirement which will add to the difference.
We have not offered performance warranties, I simply have educated folks on bin reports and ask them to call me if the operation doesn't agree with the prediction. What that means in short is if your load is 60MBH and the outside temp is 42* we expect your equipment to run for 41% of the hour with a 3 ton. In other words if your experience was dramatically different I would expect you to call.
Best bet is to grab a coffee have a sit down bring what you have and we will dissect the calculations and root out disparities.
Without using this forum to discuss the merits of others I will tell you the job I'm going to wrap up today is across the street and a referral from someone who employed one of your other bidders.

For the others: a portion of the load comes from a walk out basement which doubles the square footage in play as well as the builders desire for more than minimum air changes.

Masoud, thanks for the kind words. The tip you sent me (while uneccessary; I'm grateful) was applied to the purchase of my new guitar with which I will punish listeners for years to come. I passed by your home yesterday as we will be digging on Seymour next week. I don't think we'll really be sure on your Climadry 'til next year but I'll be nearby if you need us.
Joe

OK, the walk out basement bumps things up a bit.

I was definately remiss in not thanking the rest of you for the kind words.

I will add that Chris was concerned that tightness of the house and additional required air changes seemed to create additional load.
I was more than a little inarticulate in explaining that many houses have less than healthy air changes and that more is better even if it adds a touch of load, but his question in short was essentially:
at what point does tight began to cost more than it gains?
J

There is always a point past which decreasing infiltration or adding insulation makes little economic sense.

One of my longer term research projects is to learn about smart ventilation - using CO2 or other sensors to right size the amount of fresh air to maintain IAQ rather than mindlessly blowing and conditioning outside air 24/7 in pursuit of an ACH or CFM standard.

Curt, Whenever you figure that one out, please let us know. I was asking myself the same question, but was not willing to allow it to become one of my longer term research projects. Those passive houses in Germany look great on paper, unfortunately us humans need a certain amount of air exchange. There are now several studies from Germany and the US which attribute the raise in asthma and allergy to the increase in airtight buildings and the subsequent exposure to the amount of specific mold antigens (and I am not talking about the ones which are visible). Germany is interesting in that aspect since it had the unique situation. The population was separated into east and west germany, separated by the wall. So they all came from the same genetic background, but were forced to live under different environmental condition. East germany, much more pollution, highly inefficient buildings, much air intrusion. West germany air tight, very clear outside air. It turns out that the rate of asthma and allergies were 60% higher in west germany. 10 years after the wall had come down (after they all went and updated their building tightness with a lot of federal grant money), they repeated the studies, east germany had caught up to west german allergy and asthma levels. Multiple subsequent studies in the US and Germany are now finding a direct correlation to the indoor exposure of a specific mold called alternaria, which seems to activate the patients immune system to become more sensitive, which in turn manifests as asthma and allergy in the respiratory track.

As you all know I am among the less learned here, but it has occurred to me that mold, asthma and the like occured less in grandma's leaky scarcily insulated, poorly glazed single pane windowed house full of smokers.....
j