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