hello all!

been a lurker for a while, learning a lot, but I have a couple specific questions that I haven't been able to find answers to while searching/reading..

My wife & I are building a house this spring - approx 2000 sq ft ranch w/walkout basement.  We live in Northeastern WI (Green Bay - GO PACK GO!!  )

Anyway, she was hesitant at first but is now fully onboard for geothermal.  We are planning to build a very tight house - 5.5 inches of urethane foam in exterior walls, foam + batts in attic, probably double-paned low-e windows, etc.  Basically going a bit overboard to build an energy efficient house.  I know that our initial costs will be higher, but as oil/gas prices go up, I consider it insurance.  we plan to stay in this house long term (to quote my neighbor, "they'll take me out of here in a box")

finally, on to the questions.  In my initial conversations with heating contractors, I've gotten some conflicting info about a couple things.  First is the use of auxillary heat.  I've been told that there is no way geothermal will provide 100% of our heating needs, that we will need aux heat source.  I've also been told that because we are building the house so tight, we should be ok without auxillary heat.

I realize there are other variables, but I'm concerned about getting answers that are the exact opposite of each other.

Also, we are still considering a photovoltaic system for electric.  We won't be able to generate 100% of our need, but would be able to generate a good portion (>50%).  Because of this, the next decision has to do with hot water.  If we use PV for electric, I'm inclined to go with electric water heater, but if we go with gas (considering AO Smith Vertex 50 gal), I'm not sure how that can mesh with the geothermal for pre-heating water.

Kind of rambling here, these are probably the first of many questions - but I found a GREAT site & I'm going to exploit it!  

You don't want the geothermal to do 100% because the unit will be oversized. Oversizing means a longer return on investment and a fridge effect, which is uncomfortable. Research thermostats like the Honeywell Prestige HD that allow you to disable the aux. heat or also lower the temp. it will kick on, ie. it won't kick on unless it's below 20 F. If the house is tight you will not need much aux. Check refs and get a good installer and you will be fine.

Water heater: Most hear say you need two hot water heaters. Search and you'll find Bergy's piping config. for the two water heaters. Get electric for the unpowered tank (or a pricey unpowered Marathon) and whatever you want for secondary. Gas will beat electric but consider the GE 50 Heat Pump water heater if you want to avoid gas. Gas and power vent is almost the same price as the GE HP. If you already have a chimney, then it's hard to beat natural gas. Cheap, reliable and very fast recovery.

The heating contractors are dead wrong, it's completely possible to design a house with a large enough Geothermal system never to require aux heat. However, is it worth it to design a heating system that cost an extra 20k as opposed to designing a smaller system with Aux heat that would have to be utilized on only a few of the coldest days a year? Probably not. You will never see a return on the additional investment. It makes far more economical sense to design a system that would need to use the AUX heat a few days a year. The additional cost of operating the system during those days is very minor compared to the overall efficiency of the system.

Regardless of how tight you house is, I think it's a very bad idea to not have AUX heat. What if your water pump goes one cold winter night? With an AUX heat, you can keep your house warm a week until you can get a replacement water pump ordered and installed.

Also be aware there are rules of how tight you can design the house to be before your required to bring in outside air for ventilation. It's completely possible to make a tight enough house where you suffocate in your sleep when you use up all the oxygen in the house.

Electric heaters work fine with Geothermal systems, I have one myself. The Federal tax credit Requires you to have a Desuperheater installed on your geothermal system to pre-heat your hot water. Also most state rebates require a desuperheater as well.

Aux is also cheap (i.e. cheap to have, expensive to run) insurance to have in the event of a system problem or geothermal lockout (to protect itself). I have and like the Prestige thermostat that dkubarek mentioned. The aux lockout can go as low as 5 degrees F. You will need an outdoor temperature sensor that works with the thermostat you choose. Honeywell makes a wireless outdoor sensor for the Prestige. There are other thermostats that have an aux lockout feature, but make sure you get one that can be set to the lockout temperature that you need. Some only go as low as 40 degrees (not low enough in my opinion).

Whether you need 1 or 2 electric water heaters depends on your hot water needs, timing of those needs, recovery rate, tank efficiency, tank capacity, electricity cost, etc. You can see a lot of information under the thread "Justifying two electric hot water heaters". With a gas water heater, I would get a buffer tank. With an electric water heater, it's best to crunch some numbers to see if the buffer tank will be justified in your particular situation. It wasn't for us, but it is for many.

Keep asking questions!

Consider foaming the attic sheathing and sealing it so attic becomes a semi-conditioned space.

Make sure a proper load calc is done reflecting your high-end building material choices.

Plan on a blower door test to prove the tightness - it is easy for sprayfoam contractors to miss spots.

Plan for some mechanical ventilation.

If you at all value summer cooling comfort, that is, good dehumidification, you'll want a unit sized so that it isn't way oversized for cooling, which in Wisconsin means a bit undersized for heating, and you make up the difference with a bit of aux heat

PV is becoming more competitive, particularly in states with robust net metering rules. The PV decision has NOTHING to do with deciding how you heat water, unless you are off grid.

I'm a fan of heat pump water heaters, but they need a fairly decent sized room to work in, not a closet. They cool and may dehumidify the room they are in. They are new and pricey; long term dependability not yet proven. I have an external Geyser unit, however the GE might be a better choice for new construction

A 2 occupant household wanting to use a desuperheater without two tanks might get by with a single large electric water heater with the lower element thermostat set substantially cooler than the upper. The combination of a desuperheater and a heat pump water heater has very high first cost but very low operating cost; however, with 2 occupants payback on such a system is likely to be on the order of several decades.

Geo systems provide 100% of your needs in on 1, 2 or 3 stages.
2nd or 3rd is auxillary coil. The "geo can't give you all you need" argument is born of ignorance.
Ask bidding contractors to show you different size comparisons.
We do not recommend a desuper heater without a buffer tank though there are occasional examples that it might work.
Type of water heater is dependant on goals and fuel available though I caution folks to be leery of the false economy of gas tanks that heat water for less but burn air from the home that you pay to condition and pay to replace.
Good luck,
Joe

Jerkylips: As a homeowner, not a professional, I'd like to share my experience from last winter in Upstate NY.
When my contractor spoke to me about my geo system NOT covering 100% of my needs, I was skeptical and asked him why he didn't have the confidence in the system. After several discussions he was able to share his in depth knowledge enough to convince a regular homeowner and I went with the smaller 3 ton unit that would only cover 85-90% of my needs. He also installed the backup electric coil.

Even though I trusted his expertise, I went into the heating season worried about exploding electric use. I installed submeters on my geo system, my electric coil backup as well as my hot water heater. I took daily data for the entire heating season. The data that I have backs up my contractor plus some!

My electric coil backup (or stage 3 as Joe mentions) was used on 23 days during the season. It used anywhere from 12 to 124 kwhrs per day on those days. When the 124 hit, boy was I concerned, but it was just one day and it was following a period of 2.5 weeks of less than freezing temps.

This may sound scary, but when you look at the BIG picture, I spent a little over $800 to heat my home ALL season. This includes the geo costs as well as the electric coil backup. My home is 1950 sq ft and is 80 years old. In the previous 4 years I had used approx 1000 gallons of fuel oil to heat my home costing anywhere from $2,500 - $3,200 per year. Furthermore, in those previous years we kept the tstat at 58 degrees, with geo we keep it at 64.

My point is, if I wanted to cover all my heating needs with a geo, the estimate was ~$21,000 more. I used 892 extra KWhrs in the season as stage 3 (electric coil), at 12 cents a kwhr that equates to approx $107 dollars. Given that data, it would take 210 years for me to pay back the extra $21,000 for a geo system that would cover 100% of my needs.

Obviously it is possible to meet 100% of your needs with geo, the question is, do you really want to?

Great data. The $21k is better off in the bank. Even at a paltry 1% interest it more than covers the additional cost of power.

Great info Ona.... thanks for posting

wow, you guys are awesome!  thanks for all of the great info.

just to clarify a couple points, the conversation I had with the heating contractor was brief, over the phone.  We're nowhere near the design stage.  In retrospect, he may have been telling me what you guys are saying, that I don't WANT a system that will provide 100% of my (our) needs.  It was more of a warning - "some contractors may tell you that their systems will provide 100%, BUT..."  I've had this company do work on our old house & install a furnace - I'm confident that they are reputable & knowledgeable.  Thanks for the heads-up, though!

 

As for the electric vs. gas, the main reason I'm asking the question is economics.  I'm trying to figure out if I can justify the PV system.  I was set to go that route, but our utility company (WPS) recently ended their net metering/buyback program so now the payback will be longer.  Just trying to figure out what makes more sense - paying for the gas to heat water or getting an electric & using the electricity we generate. 

the idea that there is a false economy because of the heated air being vented out is something I hadn't considered, so thanks much for that.

Oh...and we definitely will install an HRV.  I realize that will reduce efficiency, but air quality is more important

Does you wife have a sister? Cause is I try to lower it to 66 I get yelled at. 64 degrees is the divorce territory. At the 58 degree mark, I would not trust her sleeping next to me, I might now wake up the next morning.

I pretty much keep the Geo at 68 now, I might lower it to 66 if were hot or up to 70 if were chilly, be generally it says on 68 most of the time.

TechGromit ~ Don't worry, I'm not offended... but I AM the wife - and I have no sisters :o)

And yes, being a California girl, my husband pulled the wool over my eyes for 4 years telling me that "everyone" in the northeast set their tstats at 58. I was bundled up in wool socks and layers every evening. After 4 years we WERE close to divorce over the matter and that is when we installed geo. So, even though I was slow on the uptake, I not only have a better heating system, but air conditioning as well. The problem is that we are both enginerds and too practical for our own good... so even though I was freezing, I put up with it because of the cost of oil.

Just realized I had one additional question that I forgot to ask.  I was told that it is possible to use a water heater as the emergency heat source rather than heat strips.  In addition to electric or gas tank-heaters, we are considering a tankless. 

Is using the water heater as emergency heat possible?  If so, is it a good or bad idea?  What about tank heater vs. tankless?

Jerkylips,

First things first... GO PACK GO!!!

Living in Green Bay puts you in a heating dominated area. Generally speaking (remember, every home IS different) you will need twice the amount of energy to heat your home as to cool it. Because of this, Geothermal will be a balancing act between heating and cooling. If you were to install a heat pump large enough to heat your home without needing Aux. strip heat the system would be WAY oversized for the cooling needs. During the summer, the Geo would come on and quickly cool the home not allowing enough run time to dehumidify, resulting in a cool and CLAMMY home. A VERY uncomfortable living situation! Aux heat strips also serve as an "Emergency" backup heat source in case of a system failure.

You will need to check with your electric provider about rebates or reduced electric rate programs. Some providers in Iowa REQUIRE twin electric tanks to qualify for their programs. Personally, If natural gas were available, I would opt for a 50 gallon un-powered electric as a buffer tank with a gas water heater, sized to your needs, providing hot water to the home. If propane is the only thing available, I would opt for twin electric tanks. Make sure your plumber understands the concepy of a buffer tank and have them piped as shown.

Bergy

thanks for the reply & the diagram!  you guys are all a wealth of knowledge!!

I realize that this is probably a REALLY dumb question, but I've read about "buffer" tanks and "unpowered" tanks, but then I read stuff like you posted, about "unpowered electric" tanks. If it's unpowered, then why is it electric?

You would buy an electric water heater to use as a buffer tank for the desuperheater. To get full efficiency from this tank, it should not be powered. You can run power to it, but keep the circuit breaker to it turned off (unless you need extra hot water capacity when you have visitors, for example). You should size the tanks so your normal hot water needs needs will be met without powering the buffer tank. Electric water heaters can be cheaper than buying a water storage tank that is called a "Buffer Tank" by name. Serves the same purpose. Not a dumb question.

WHY is that?????  Only 1-2 mfg's??

I don't really know. I assume smaller production runs compared to water heaters. Possibly marketing. Since May of this year, I don't recall ever seeing a suggestion here for anyone to buy a buffer tank from a geothermal manufacturer (only unpowered electric water heaters.) I do recall a person starting a thread about being dissatisfied with the heat loss of a storage tank from one geothermal manufacturer (Water Furnace). If you want a premium water heater (expensive but has a lifetime warranty) get a Marathon. We have an 85 gallon unit. Heat loss is rated at 5 degrees per 24 hour period per the manufacturer. Payback is questionable, but for us the warranty and no steel tank was worth the price. I'm one of those single tank homeowners, by the way.

I found that thread that I mentioned earlier. Here is a link. Don't know how they ever made out.
http://forum.geoexchange.org/viewtopic.php?f=2&t=1280&p=10194#p10194

P.S.  We purchased 2 Water Furnace geothermal units in April and love them.  I wouldn't be turned off by this one thread about WF.  From what I understand, 1 degree per hour of heat loss is not bad by conventional water heater standards.

TG, you kill me!
They only thing we don't worry about much at our house is the heating or cooling bill. the higher it is the (geometricly) more money i make. Perhaps your wife should meet a suave mechanical contractor...
j