Texas Geothermal for Modest Sized House Questions

Here is an idea.

If you want to heat your floors with solar, and you are in a favorable climate, do it directly using flat plate solar collectors, a storage tank, and circulating pumps. This is much more efficient than converting the solar energy to electricity, storing it in a battery, then converting the DC current to AC current to provide electricity for heating.

You could also use this to heat your domestic hot water using a solar water heating tank that uses a separate internal heat exchange loop inside the tank to circulate the solar heated water to heat the domestic hot water.

Then install a high efficiency air-source heat pump for your cooling needs. In your area with relatively high ground temperature, a ground source heat pump is only marginally more efficient than a top of the line air-source heat pump for cooling needs.

If you will have propane available, you could install a small propane boiler as a backup if conditions are not favorable for solar heat generation (more likely in winter when you will need heat than in summer when you will need cooling). You will likely need at least a small electric generator available as backup using propane as fuel for the generator. Buy a large enough propane tank that will carry you through the year and have it topped off during the summer when propane prices are generally lower. If you are thinking that you won't need a backup generator, think again. What if a circuit board in your inverter fails and you can't get a new one for a week or more? Can you live without any electricity for a week or more? Also, we have many 10 year rated batteries installed where I work. We routinely have to replace them every 5-6 years because they fail load testing. And these are backup batteries maintained on float in pristine conditions and rarely if ever put under load except for testing. That 10 year battery rating/warranty is more of a sales tool than reality. This is additional PV system downtime you will have to factor in for battery replacement.

 

Hmm. You know, I always frown when someone says 'good luck' as if my chances of success were slim to none. This is sunny Texas we are talking about here. You make it seem like I am trying to go off grid in some place like...I don't know, Canada or Alaska. Solar WILL work. ::shrugs:: Nevertheless, I suppose I can accept the 'best wishes' and 'good luck' as sincere responses.

Much Appreciated.

I think I have received as much information as I am going to get from this forum. I am going to call around locally to check prices and speak to some real geothermal experts to see whether or not it is feasible in the area which I plan on building.

For everyone who took the time to respond to my thread, thank you very much. I came here knowing next to nothing about how geothermal works, but now I have, well I won't say, 'better' or 'more clear', just...I am leaving with more than information than I came.

I will still be around if you have anything else to say to me, but I prolly won't post anything new until I have a few quotes to see if they are good.

 

arkie6: I can live without power for a week, no problem. I won't be using my propane tank for anything other than cooking and washing. Indeed, there is a such thing as rush overnight shipping for spare parts or even new equipment. I know you are trying to think of worse case scenarios, but in this age, it doesn't take that long to receive new parts.

I regret mentioning that I am going to use solar. Can we please stick with my geothermal questions?

Thank you for your response.

 

You don't know the size of your system.

But you don't have the budget for it, so its not really worth anybody figuring that out for you.

Phone your local guys and ask them what they can do for that budget. If they bite, you have a chance.

You'd be looking at 25k around here. I could do it for 15K for myself (free labour) only by poaching a bunch of stock off myself.

 

Skip the floors, put an air source heatpump in there (or a couple mini splits) which heats and cools, run it with the electricity from your solar system, enjoy life in sunny Texas....
Put in a heat pump water heater. Stay a couple thousand $$$ below your budget.

 

urthbuoy: Oh well I certainly wouldn't want you to do that. It's not as if we were good friends or family members, after all. 25K? Hmm. I don't know. That might be doable, but I would have to get quotes from a building contractor to see how much it would cost to build my house first. If there is anything left from that, I may be able to put more into getting what I need.

You are absolutely correct that I do not know the size of my system. All I have is the square footage of the house that will be built, and the materials that it would be built with. I thought maybe that would be enough.

 

If solar electric is a done decision, I think you are probably much better served with ductless minisplit heat pumps. Perhaps two units, one for each floor depending on room layout and ability for air to communicate between rooms.

You may be much better served at website www.greenbuildingtalk.com to give you more focus on insulation and envelope improvements before getting to discussion of heat source. The house you discuss seems very notional at present. Your best investment of time and effort at this point (having already decided off-grid solar is the path forward) is trying to reduce the peak energy demand. The return on investment in terms of energy efficiency, power requirements, environmental impact, and costs is much better in ensuring the envelope and insulation are sound. The cheapest kwh of energy is the one you don't use.

In many situations, geothermal heat pumps are the most efficient way to meet HVAC demands. In your situation of new design/build, efficient design and considerable investment in reducing heat loads is the way.

I'd encourage you to focus as much as you can on mini-split Heat Pump units (Daikin, Fujitsu, Mistubishi, LG.) At the other site mentioned, I'd encourage you to take any posts by Dana1 as gospel truth for reducing your up front requirements. If radiant floors are an absolute must, look at Daikin Altherma air to water heat pumps.

Don't give up on efficiency, but maybe place more consideration on something other than geothermal.

 

mtrentw: Wow, that was the best piece of information I have received yet! Thank you so very much for your input! Yeah, I have already chosen to move most of the high energy using appliances (cooktop, oven, clothes drier) to propane, so it can be off the solar grid. I also plan on using LED lighting throughout the house. I will take your suggestions to heart and follow the links you have provided. Again, thank you very much for the valuable information.

 

Why don't you switch back the appliances to electric and get a bigger solar roof?

 

Because those items use a lot of energy, and I don't want them to be on the electric grid.

 

The energy they use is the same with gas or electricity, maybe even more with gas. It is just electricity instead of gas as a energy delivery medium.
However, the electricity you can make yourself, the propane you likely cannot.

 

I agree, but propane is inexpensive. In addition, because I will own the propane tank, this allows me to choose my propane supplier instead of being on a contract and/or being strongarmed because the propane company owns the tank. Using propane along with solar is an appropriate balance.

 

I'm not overly fimiliar with off grid solar.

Question; how big of a battery bank do you need to make it through a cold night with a geothermal compressor running from sun down to sun up? Is it even possible?

 

I am not entirely sure myself, as I know very little about geo tech. I do not know what the energy requirements for such a system is. I would have to find that out, and perform a few quick calculations, then add ~10% to account for a reasonable margin for error to come up with an answer. As was suggested to me earlier, I am doing a lot of research on these mini-split Heat Pump units and I am highly interested in the technology. The good thing about solar is that it can support just about anything so long as you have an appropriately sized grid and battery bank.

 

another benefit of two 1.5 ton (or 1 ton if you put the effort into insulation and air sealing) is that if charge and battery conditions dictate, you could prioritize load and only engage one of your heat pumps.

I still think you are in the wrong neighborhood trying to find heat systems. You should be looking for an optimized design first. Best suggestion at this point would be to look at BEopt software from Department of Energy. Free download to help you optimize and make adjustments and tradeoffs between envelope and heat plant. Off-Grid solar will be a driver though and probably steers to minimize heat load through envelope improvements.

https://beopt.nrel.gov/
The BEopt™ (Building Energy Optimization) software provides capabilities to evaluate residential building designs and identify cost-optimal efficiency packages at various levels of whole-house energy savings along the path to zero net energy.

 

mtrentw: I already have the general design of the house. It's a pretty much square 2-stoey layout with a single garage. I was told that the fewer outer walls that the home has, the cheaper it is to build, so I am keeping things simple. There really isn't anything special about the shape of this floorplan. Also, I think this will also enable me to optimize this 'envelope' that multiple people have mentioned. What do you mean that I am in the 'wrong neighborhood'? Do you mean because I am still chatting in this forum when I should be elsewhere? I am not going to ignore people if they ask me a question here. I have already created an account on GreenBuildingTalk, and filled out the information for a free estimate.

 

Wrong Neighborhood - While this is the best and most comprehensive geothermal site, with the best assembly of professionals in this field, I think you should not be focused on heating system design until you've focused more on optimizing your heat load. BEopt will help with numbers, but without numbers, my gut says you will be better served (on an ROI basis) by making insulation improvements which are not a major focus of this site.

You have put yourself in a tight box with a desire to be off-grid solar. If that is the prime directive, your focus should be on reducing peal electrical demand. You mentioned steel structure and framing and others have advised about needed focus on exterior insulation. I absolutely agree with previous post that you need to focus on getting as much exterior insulation outside of your framing since the steel framing is a huge conductor and diminishes effectiveness of fill insulation. The geothermal experts here can give world class advice on geothermal, but you need more focus on exterior insulation and sealing. While many of our experts here can give good insulation advice, many recommendations are very regional. At the other site, I have named an expert who can give adivce about best practices in any climate zone who has much expertise in mini-split heat pumps and regional differences.