New Construction HVAC decisions. Geothermal vs. alternatives with upgraded envelope.

[techman]

Something to keep in mind. Geo units are available as a water-water unit. They are used with radiant heat. The thing to consider is that the radiant tube density will be higher to accomodate the lower (130 deg) water temps.

paul

 

[Raspy]

Paul,

How much improvement is there in system efficiency when the delivery temp is reduced to about 110 degrees for radiant, from the delivery temp required for the forced air system, what ever that is?

 

[MGH PA]

Thanks for the tips. I know the one contractor that gets good reviews in the area (who have been conversing with a lot) said they don稚 typically do the load calculations. They have a third party do it when requested, but it is expensive. So that threw me off a bit

Anyone who is giving you a "size" per your HVAC system, ask them to see their load calculation. Personally, for that kind of money on a Geo system, particularly per the fact that this is new construction, you shouldn't have to ask for one IMO.

When looking for a geothermal HVAC contractor, one standard I'd try to ensure they met is that they're a member of the International Ground Source Heat Pump Association, and verify that they took took training. Absolute worst case, ask the HVAC contractors for references on previous jobs they did and contact the homeowners yourself. A contractor who does good work and stand behind what they do generally has no problem giving out references and the people they do work for don't mind sharing their experience. Because of this, 28k for a new install for new construction isn't way out of wack depending on the quality of work IMO. However, what scares me is no one is willing to go over their load calculations with you.

Geo is genearally rated in EER for cooling and COP for heating (not SEER rating). a 20 SEER fully modulating forced air AC/heat pump system may have around a 13 EER rating. A mid tier geo unit generally starts out around 30 EER. World of difference per performance.

 

[MGH PA]

The one company quoted me a radiant system add-on to the Geo and it was a littler over $12k. Way too steep for my blood.

Something to keep in mind. Geo units are available as a water-water unit. They are used with radiant heat. The thing to consider is that the radiant tube density will be higher to accomodate the lower (130 deg) water temps.

paul

 

[MGH PA]

MGH,

You mentioned Creatherm panels in the basement for hydronic radiant heat. Does that mean you'll be putting down a topping slab over the structural slab? If so, I'm wondering why? Why not put the tubing in the structural slab?

What about the main floor? Radiant there too? And again, if so, how will you do it?. The best way I've found is to staple the tubing directly to the subfloor, double plate all the walls, and pour a thin slab the thickness of the lower plate, typically 1 1/2". This gives you a radiant floor that will accept any flooring material and offers some mass for temperature stability. You can tile directly over it in the bath, or tile the whole house. So, you save money on the installation, you save putting in a tile mortar bed in the bathrooms, you get a stable heated floor everywhere and you can design the heat well because you are not locked into a defined tube spacing of the Creatherm panels.

You also mentioned the hydronic system would be later, but again, why? If you want tile, you'll need the hydronic floors or the tile will be very uncomfortable. I don't get why you would want to deliver the heat with blowing air, instead of with a radiant floor system that you are already planning anyway.

Have you done research to find the long term cost of maintenance and the reliability of GS systems? Maybe some others can chime in here too. I'm not saying one case is indicative, but my neighbor put a system in and it has not been reliable or cheap to operate. In other words, it has not lived up to its promise. If cost is a concern, a few service calls can certainly offset the savings you might get through a lower cost of operation. And each of those calls means a period without heat.

With all systems, you have to look beyond the theoretical efficiency and factor in reliability. This can vary wildly between different manufacturers as new products become available and contractors take them on. Manufacturer's reps, visit contractors and architects to promote new products, that then get spec'd in the plans, but have no track record. In my hydronic heating business I have been burned too many times by the newest, and seemingly greatest new products that did not prove to be reliable. All of those cases cost me dearly in warrantee repairs and somewhat in reputation. Be sure you understand the reliability and parts availability of any complicated system you choose.

Raspy, the creatherm panels are an all in one solution (insulation plus channels for the pex. Less complexity than tying into rebar, and it doesn稚 crush under the weight of workers putting in the concrete.

Your reliability argument is definitely a major concern of mine (hence the post). The Geo systems seem overly complex and expensive to fix should problems arrive.

As adding the radiant later, I need air conditioning regardless, and one of the main reasons I didn稚 want to do radiant heat/central air, is essentially needing two systems, and ductwork run regardless (unless I use a mini split style system).

I suppose I知 not opposed to other solutions, I just don稚 know what the best all around price/performance aspect is going to be. I know I want it to be comfortable, efficient, and clean.

 

[Sigarms]

Thanks for the tips. I know the one contractor that gets good reviews in the area (who have been conversing with a lot) said they don稚 typically do the load calculations. They have a third party do it when requested, but it is expensive. So that threw me off a bit

Any decent HVAC contractor generally uses Wrghtsoft for load calcs and does it themselves. A good company will at least do a block load on your house even for retrofit to ensure someone really didn't screw up before them (lots of times if the homeowner has no complaints with an existing system, the assumption is it is sized right to begin with).

When you charge a premium price to stand behind your work and ensure you customer is happy, in the HVAC business, ensuring you have the right load for the equipment is kind of important LOL

New Construction homes in NC are required to have at least a block load done and kep on file. Not saying the inspector actually knows what he's looking at, but at least they require it.

At worst, the HVAC company you're dealing with is kind of doing wrong IMO. They come in with what size they think, but for over 20k, they should eat the load calculation IMO if you decide to go with them and feel more comfortable actually running a load calc. Heck, they should be able to ball park it and if you sign with them, should do the load just to cover their butt. Again, that comes with charging over 20k for a job and standing behind the work.

Thing about load calcs and what you have to be careful of, is it's garbarge in, garbarge out, and if anything is missed, it can throw it off.

Old school tip... 600 sqaure feet per ton, and if the load calc don't come up to that, you missed something:laughing: In all seriousness, part of the reason for the load calculation is to help determine the duct size per room to room.

 

[dodge man]

Unless I'm missing something, I think the load calculations are pretty standard. I know when they sized ours it came up where they could have gone with a smaller size but it was close so they stepped it up to a 4 ton. I realize housed depending on how they are built can make a big difference. Also the AC side of geo is pretty cheap as it was explained to me. We also went with the two hot water heaters with the desuper heater being in one unit. Kind of ironic but the colder it is outside the more "free" hot water you get.

 

[Sigarms]

Unless I'm missing something, I think the load calculations are pretty standard.

As mentioned, garbage in, garbage out (also depending on where you live at what what design temps you're using).

Generally with multi / variable stage compressors for your condensing unit, you do have some leeway to oversize.

With mini splits, in my neck of the woods, I will always size accordingly for heating if there is no supplimental heat, which tends to oversize the AC (and sometimes by a good bit depending how close to Tenn or Virginia the home is).

 

[Raspy]

I don't think not doing the heat load calculations is necessarily a deal breaker. I designed a lot of hydronic heating systems and went more on BTUs/sq. ft. in given areas that I knew well. Some variations that swayed the decision one way or the other a bit were how many zones, particular lifestyles, house on a slab or not and flooring materials. None of those fit calculations about BTU losses that had to be factored in.
But you should make sure it's not some guy just shooting from the hip and covering himself by oversizing. He should know your area and have a track record of good working systems to back his claims. The very best advertising is word of mouth.

 

[techman]

Paul,

How much improvement is there in system efficiency when the delivery temp is reduced to about 110 degrees for radiant, from the delivery temp required for the forced air system, what ever that is?

About a year ago I helped a co-worker put in radiant heat pump. I believe he designed for 120 deg water, which involved about 25% more (if I remember) greater tubing density. The water temp. The water temp is a function of a number of variables, like flow rate, temp differential in the unit, etc. End result was no problem heating. We installed a 50 gallon water heater as a storage/buffer tank. It kept warm water available as soon as the circulator starts. We also wired the water heater heating element as the backup heat for the system. For AC a couple of zone valves directed the water (now chilled water) to air handler designed for chilled water (coils, etc suitable for water). Last I asked he was very pleased with operation and efficiency. I believe that the efficiencies are comparable to the air units.

paul

 

[kenmac]

skip all the duct work and go VRF. You can supply multiple inside units from one outside unit, and there is no loss of air flow, heat, A/C through the duct work. In fact, no duct work at all !
Some are good for 80% capacity @-22 and 100% @-4 deg which depending on your heating needs, could eliminate the need for any back up heat

 

[Raspy]

One of the things I've seen over and over is the forced air guys want to add a backup system "just in case". One of the justifications for this is that the radiant system takes so long to heat up, or may fail. Of course, this argument is being put forth by someone who knows nothing about radiant and wants to sell more equipment. It often works. But later, when talking to the homeowners they eagerly say they never use the forced air and don't like it. Or they simply say the radiant is their favorite feature of the house.

In this case there is already a backup system. A fireplace. It may not be the first choice, for a number of good reasons, but it works and requires no power. So, it may be possible to reduce the cost of the forced air system and get the radiant on line in the beginning.

 

[newbury]

Thanks. Very help as usual. I�･ making it a point to have great air sealing to help cut back on infiltration. We are using ZIP, and the NuWool is a damp spray that gets put in AFTER all seams and penetrations have been sealed. Part of me feels this should be more than sufficient, but I also worry about thermal bridging.

I�･ going to have all utilities placed in the basement central located for what it逞ｴ worth.

I just get frustrated because we live in a è*�熔w tech area where I feel like most of the subs are used to building what they豎*e used to and scoff at the newer ideas (like the use of Manual J逞ｴ to properly size an HVAC system).

My GC is great about staying up to date with current building methods, but in the areas he subs out, I�･ finding even his good subs don� know all I want them to know to complete some aspects of the project.

When I�･ paying the bills, and I want my house to perform a certain way, I�･ going to be extremely disappointed if it doesn� because some sub didn� or couldn� bother to stay up to date on proper building science.

You write like an educated person. I've lived as an adult in Northern Vermont, Virginia and Mississippi. I own land and have hired contractors in all three. I think it is pretty universal that most GOOD contractors don't like to experiment and use the latest building science unless it is a sure kill. It's usually more expensive to come back and fix something than to put in something you know will work.

What is your target room temp for heating? Some people need it at 73 degrees F. Others can live at 65. I set ours at 60 for the winter, that's what we like. I don't turn it down when we leave the house unless we are going to be gone for days. (And for the cooling I used to set it at 80, then 78, but the wife revolted and now 75 is the compromise.) But if you design a system for heating to 73 it will probably be cycling it too much for 60.

I'd strongly recommend against going with 1 "system", put in a woodstove for when your motor fails or something messes up on your main system.

 

[JamesHW]

We’re dealing with decisions for installing a heating system from scratch, although in our case it’s retrofitting an 100+ year old Upstate NY seasonal brick house last heated with coal stoves. GeoThermal with horizontal loops was an early fav but has faded from consideration somewhat. Research showed sand, while one of the best conductors when wet, is one of the worst when dry. The house has a massive chimney in the center, but a fire that burned the roof off, we think in the 20’s (family stories are vague). In any event the solution we end up with needs to be workable for my wife if she is alone, so wood burning stoves are low in our consideration. No chance of pushing air through ducts from a furnace unless we go with a high velocity tube system, but generally impractical & expensive. Low profile radiators mounted on exterior walls under the windows and a furnace in the basement seems our best play, maybe supplemented with electric fireplaces that take advantage of the two sided fireplace (kitchen & front parlor). In any event we’re starting by sealing up the house and insulating the attic as best we can and moving forward with good, double paned storm windows. We also have an 800 sq ft wood 1 story uninsulated wood addition to consider, but figure short term a good old wood stove would work best and any central heat considered separately from the main house. Perhaps by the time we get to that phase their will be some new options to consider.

Didn’t want to hijack the thread, but I always learn something new. Thanks!

 

[jk96]

Old school tip... 600 sqaure feet per ton, and if the load calc don't come up to that, you missed something:laughing: In all seriousness, part of the reason for the load calculation is to help determine the duct size per room to room.

I think my HVAC guy used the old school tip. That's why I ended up with 8 tons when I needed 4-5 at most.

 

[MGH PA]

You write like an educated person. I've lived as an adult in Northern Vermont, Virginia and Mississippi. I own land and have hired contractors in all three. I think it is pretty universal that most GOOD contractors don't like to experiment and use the latest building science unless it is a sure kill. It's usually more expensive to come back and fix something than to put in something you know will work.

What is your target room temp for heating? Some people need it at 73 degrees F. Others can live at 65. I set ours at 60 for the winter, that's what we like. I don't turn it down when we leave the house unless we are going to be gone for days. (And for the cooling I used to set it at 80, then 78, but the wife revolted and now 75 is the compromise.) But if you design a system for heating to 73 it will probably be cycling it too much for 60.

I'd strongly recommend against going with 1 "system", put in a woodstove for when your motor fails or something messes up on your main system.

Target temps probably would be around 72 in the winter and 68-70 in the summer. I would definitely want our master on a separate zone since we sleep with it cold all year long.

We will definitely have a wood stove, I just don't want to rely on it for primary heat

 

[EddieWalker]

I think it is pretty universal that most GOOD contractors don't like to experiment and use the latest building science unless it is a sure kill. It's usually more expensive to come back and fix something than to put in something you know will work.

Solid advice. With the government getting involved in Green Energy, and subsidizing so many "new" technologies and methods, it becomes very difficult to know which will work, and what is just a fad, or even worse, a method to get Federal Funding. This is especially true with Solar and Wind technology. You don't know what you are getting, how long it will last, and if there will be somebody that will even work on it in ten years. I've seen this with plumbing more then anywhere else, but I don't do HVAC, so I can't say how many "experimental" systems are out there that people will regret having down the road. How many people fell for the pigtail light bulbs that where supposed to save so much money and save the environment?

 

[NorTracNY]

Am I gathering it correct that you're looking at geo, but not do radiant floor heat? I understand the radiant heat is a little more expensive (labor cost is a little higher), but with new construction, I'd value the radiant heat over geo. I was lucky and learned about radiant heat before we built. Definitely one of the best aspects of my house. You'll save money long term as you will not set your heat as high and it's more efficient.

 

[Raspy]

Target temps probably would be around 72 in the winter and 68-70 in the summer. I would definitely want our master on a separate zone since we sleep with it cold all year long.

We will definitely have a wood stove, I just don't want to rely on it for primary heat

I always design the Master with a separate thermostat too. Including the Master Bath is a bit more of a decision. If it's a large room, it can get it's own. But if it's smaller it can be with the Master and just regulated to get more heat by proportion. Then a programmable thermostat will bring it up to temp before you get up. The tile floor is the issue. If you don't have radiant heating, the Master Bath can get an electric radiant mat under the tile with it's own floor sensing thermostat. Floor sensing allows a small radiant zone within a larger forced air zone, with no thermostat conflicts. And it allows a cool sleeping area with an inviting warm bath floor.

 

[PEJ5]

There have been some great comments. We just built a garage/2nd floor "cottage" and so far the shell is up and closed in. Work on the inside will start once temps get above -18C/0F.

It was built with 2x6 on 24" centres so the there is lots of room for R22 or R24 batt insulation. Thermal bridging is still a big issue because there are a number of structural locations where 3 or 4 2x6s are nailed together, and headers that dramatically reduce the opportunity to insulate well. Based on how hot and cool you plan to run it, definitely add 2"+(R10) foam outside under your siding. Big payback, and it moves the dew point for any moist air leakage outside the framing to reduce the chance of rot. 25% of heat loss is through the basement walls so again, insulate well outside and below the concrete walls and slab while you have the chance.

As for ceiling fixtures on the top floor puncturing the vapor barrier, strap the ceiling with 2x3" or 2x4" and keep your wiring and boxes below the vapor barrier. There are many ideas for passive solar house construction that can be used to improve your construction.

In 25 years when energy cost are through the roof you will be laughing all the way to the bank.

Finally, I agree that even good builders shy away from new ideas. Share your list of specialized techniques; insist on the big ones and then be prepared to leave one or two on the table.