Geothermal

Maine Ken

I have no experience w/ geothermal heating. I have a client that is expressing an interest in it. She has a lakeside ranch. All northern exposure. Extreme winds from the lake most of the winter. What kind of heat supply can be expected from a geo system? The temperature routinely drops to -20, even -30 is more common than expected.

Any help/ advice is greatly appreciated.

Maine Ken

<A HREF="http://www.heatinghelp.com/getListed.cfm?id=346&Step=30">To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"</A>

Brent_2

geo

i am assuming you are talking about closed loop vertical wells. If you are interested in water to water than the highest water temp you should design for is 120°. It sounds like you will might need hot air to meet the loads. Do a load calculation for the house, figure the depth and number of wells, and give her the price. I am assuming this is her main house not a vacation house. the thing that helps sell geothermal in this area is the utility gives a lower rate in the winter for electric heat. The efficiencies are excellent. I am not sure how much use you have for AC in the summer.

brent

John Mills_5

Usually

get a 25 to 30 degree temp rise out of a good, scroll equipped geo. Do a heat loss to see what backup is needed. Size the geo to the cooling needs and be sure backup can handle the total.

GMcD

Geothermal

Step 1: Reduce the heat losses and heat gains on the house to the lowest possible.

Step 2: Look at geo-exchange potential from the following: open loop direct lake water (not usually a good bet due to environmental and intake/discharge issues); or closed loop lake system; is there any potential for excavations on site to take advantage of horizontal slinky coils or a combination of horizontal and vertical well geo-exchange?

Step 3: Do a seasonal (year-round) energy balance on the house and see if it needs more heating than cooling, and if so how much.

Step 4: Size the geo heat pump system for the balanced load and add supplemental heating (or cooling) as required. For the climate you are in, you are generally into a heating dominated load profile and will need supplemental heating - solar, boilers, etc.

Step 5: If Step 1 was done properly you will only need a maximum of 110F-120F heating water for general heating, and probably even less depending on the radiant/ventilation requirements. The domestic hot water will require some booster heat to get the 135-140F temps needed - possibly de-superheat exchange from the heat pump might be enough depending on loads.

It all starts with proper building envelope design and the rest gets easy after that.

Maine Ken

My client is interested. I will not be involved in design, installation, or any other aspect of geo. another company is there for that. She is aksing me for outside advice. She has an older ranch, crawl space, poor to barely adequate insulation, avg windows. FHA in place now. No means to access crawl space for piping.

What I am concerned about is needing a complete secondary system for supplemental heat. Any experience retrofitting a poor building envelope, with extreme north winds, -20 to -30 degrees very common?

Maybe I am not asking the right questions...It just seems to me that with the building as is, geo is a more southern option.

Maine Ken

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Henry_6

geothermal radiant

Hi Ken:
I've had experience with geothermal retrofits and would suggest that the starting point is the building envelope. You should not install any high efficiency system in a house that is loose in your climate. Geoff is right about the loads, but I would recommend a vertical closed loop system for the energy source designed to the proper heat load, not cooling. A correctly operating outdoor reset control with a maximum supply temp of 120 F @ design, combined with a mass tank, will give you a very comfortable system which can work well in colder climates than yours. Remember, there is no combustion air required for geothermal and, if you design an auxiliary system that needs combustion air, be sure that it is available and properly warmed( air/air H/X)

GMcD

Size for heating?

I would be cautious about sizing the geo-exchange system based on the heating load (which will be way bigger than the cooling load in most cases) unless a good soil conductivity test has determines the heat dissipation rate of the soil/well. There are many examples of geo-exchange systems that have frozen the ground out and lost significant capacity after being sized based on the heating loads where the heating load is much higher than the cooling load. Unless there is really good heat transfer and dissipation in the ground, and the ground temperature can't recover over the summer, you can slowly cool the geo-exchange system down too much over a couple years of operation.

Brent_2

From what I read it seems like the system would have to be forced air. She has forced air now, you're not going to install baseboard with 120° water, and even if you could nobody would pay to install warmboard (or equal) in an entire house.
Why would you not install a high efficient system in a leaky house? Why does it matter? You calculate the heat loss for a leaky house and provide the necessary btu's. If a house needs 100,000 btu's why does it matter if you provide it with a 70% oil furnace or a geothermal system. I would think if I had a leaky house I would want the most energy efficient system I could afford.

You should size for the cooling load and make up the heating load with supplemental heat.

brent

GMcD

So lemme get this straight

You'd rather throw energy $$ out through a crappy envelope for the life of the building, albeit in a highly efficient manner, than addressing the heat losses in the first place?? I don't know how to answer logic like that. Good luck.

S Ebels

If the building envelope is poor.......

She's not a good candidate for a Geo system. What you wind up with is way more initial investment than you'll ever recover from the Geo due to all components having to meet worst case conditions. If her btu load for heating is 100K for example and you want to meet that with Geo only, you're talking a 9-10ton unit(s). The duct sizing requirement alone will show you that it's just not feasible. Who wants 16"x36" duct running around in your crawl space/basement let alone dealing with 4,000cfm creating gale force winds in your house. (In a 5,000 sq ft house this would be one thing but 2,000? uh,uh....nope, not in anything I would ever want to be involved with)

Tell the lady to tighten up the house, get the r-value up and the air change rate down and you can help her. Not until then. You're buying trouble and so is she.

Brent_2

I wasn't talking about my own house. If a customer does not or can not improve the envelope of the house why should that eliminate a high efficient system no matter what type. You can explain why they should improve the structure but it is the customer's money. If the customer doesn't do anything to change the house then you can install any type of heating system you want to meet the load.

bren

GMcD

Responsibility

But if you know what needs to be done for the customer to secure his long term energy costs, improve his comfort, and still be able to sell a high quality HVAC system, you have a responsibility to educate the customer. Abdicating that responsibility is just taking money from shills. If you've tried your best to educate the customer and he still doesn't get it, you can continue on to sell and install highly efficient equipment into crappy envelopes that continue to add pollution, use up non-renewable resources and affect everyones health and comfort. We "comfort technicians and designers" have a responsibility to the planet first, the customer second and ourselves third if we want to maintain a sustainable business.

Craig Bergman

Agreed...

If a 2000sqft "tight" home needs a 4 or 5 ton system
and a "loose" one needs 6 or 7 tons. (just an example, a complete heat loss, heat gain still needs to be done on the home!) That would equate to about 2,000 or 3,000 savings on the loop field and 1,000 to 2,500 savings on the geo equipment!! One could do a lot of tightening up
with that kind of money. Has your coustomer checked with
their energy provider? Many have rebate programs helping to offset the upgrade costs.

Bergy

Constantin

I totally agree...

.... there is a lot to be gained from tightening the envlope as much as possible, then working on the infrastructure. The smaller the heat gains and losses, the smaller the infrastructure has to be... it's a domino effect. This is particularly relevant in older homes (like our Victorian) where there are no wet walls, chases, and other convenient built-in venues for ductwork, etc. to be hidden in.

Never mind all the space you gain on the inside if the ductwork can be hidden in the walls instead of requiring chases, dropped ceilings, and all the other "coping mechanisms" employed by crafty HVAC installers.

Besides the obvious cost benefit of going with a smaller condenser, etc. it's also a environmental benefit to go with a small, quiet unit which will be easier for neighbors (and you) to tolerate (noise), more economical to run ($$$), and easier to hide.

The decision to go with 3.5" of Corbond in the old part of the house not only stiffened the walls a great deal, it also cut infiltration to near zero and allowed us to reduce the tonnage on the AC system from 7 to 5. Should the AC system struggle in the summer time, I'll simply apply some window films to keep the sun out of the house.