Geothermal Heating FAQ

Savings from the ground up –

16 FAQ's about Geothermal Heating...

1.What does Geothermal Heating cost to install?

The best way to begin this answer is to say that it will cost more than a conventional system. How much more depends on where you live and which GHP system you use.

For ground-coupled systems (both horizontal and vertical), cost varies with the number of available contractors. Where the technology is not well established, the lack of competition results in higher prices. Open loop systems, because they do not require specialized contractors are less affected by this problem.

2. How does the cost of geothermal heating compare to other heating methods?

This has a great deal to do with your local rates for electricity and other fuels. The comparison involves the efficiency of the device, the type of fuel used and the cost of that fuel.

Obviously, it is necessary to know the total amount of heat required for the year to calculate annual savings.

Savings are also generated during domestic hot water heating and cooling. These will be small compared to the heating savings in all but southern climates.

3.How much of the job can I do myself?

Very little. The performance of a geothermal heating system is determined by the quality of the installation. Assuring that proper backfilling is done around the pipe, fusing of the polyethylene piping, flushing the system and purging air from it, all require skills, tools and equipment only available to properly trained contractors. Ground loops are not do-it-yourself projects.

5.What about domestic hot water heating?

Most geothermal heating units can be equipped (optionally) with a device called a desuperheater to partially heat domestic hot water (DHW).

In the summer, this device uses some of the “waste” heat from the air conditioning to heat hot water.

As a result, during the cooling season, this heat is free. In the winter, some of the capacity of the heat pump is diverted from space heating to heat domestic hot water.

It is important to understand, however, that the heat pump only produces domestic hot water when it is running for either space heating or cooling purposes. As a result, only a portion of the annual domestic hot water heating needs are met by the desuperheater.

The percentage of annual DHW heating needs met depends upon the run time of the heat pump and DHW use patterns in the home. The largest savings occur in applications where the heat pump runs a large number of hours (particularly in the cooling mode) and where alternative water heating is by electric resistance.

For an average family size (3.5 persons), with a 3-ton heat pump, the annual savings on domestic hot water would be in the range of 25% (colder climates) to 35% (warmer climates), or about $100 - $150 per year at $0.08/kWh.

Since desuperheater capacity is directly related to heat pump capacity, the savings from a 4- or 5-ton system would be greater than the 3-ton savings cited above.

6.Should I use vertical, horizontal or open loop?

This is a tough question to answer. Let’s look first at whether to go open loop or closed loop.

Open loop systems are best applied in situations where the house is, or will be, served by its own water well.

A slightly larger well pump is installed to provide for the water required by the heat pump.

A major consideration is the disposal of the water. Existing geothermal heating systems have used ponds, lakes, rivers, irrigation ditches, and return (or injection) wells.

Surface disposal is obviously the least expensive option; but, even if a disposal well is required, the capital cost is likely to be much less than the cost of a closed loop ground coupling.

Water quality is also an important issue. Since the water is used directly in the heat pump, the issue of corrosion and/or scaling can be a problem. If the water is hard (>100 ppm) or contains hydrogen sulphide (rotten egg smell), a closed loop system would be a better choice.

If the water is of good quality and the house is to be served by a well for domestic water, serious consideration should be given to the open loop approach.

If the system is to be a closed loop design, the choice between vertical and horizontal system is sometimes a difficult one to grapple with.

The major advantage of the vertical design is that it places the loop in a much more thermally stable zone. Soil at 100 ft is not subject to the same temperature fluctuations as soil at a 4 or 5 ft depth.

As a result, the vertical design offers the potential of supplying the heat pump warmer water in winter and cooler water in summer.

Contractor availability will be the dominant factor in determining which type of ground coupling is used for many projects. In most areas of the country, the availability of con-tractors is still very limited. As a result, if the local contractors only install horizontal systems, that is what you get.

The thermal advantages of the vertical over the horizontal are less of a factor in moderate climates. The more extreme the climate, either in heating or cooling, the greater the advantage of the vertical system.

7.Who makes the best equipment?

This is a lot like asking who makes the best car. All major manufacturers produce quality products and what is “under the hood” on most products is surprisingly similar.

One way to compare equipment is by the rated performance. This information is published periodically in the ARI (American Refrigeration Institute) Directory.

8.How do I find a contractor? 
    
Selection of a contractor for a geothermal heat pump system is very important, particularly for ground-coupled systems.

There are several places to look for information.

Local utilities often have promotional and/or certification programs for both ASHP and GHP contractors. The utility may maintain a list of approved contractors to which they can refer you .

The search for a groundwater system contractor is somewhat simpler. In this case, most general heating and air conditioning contractors can handle the installation without any special training.

It is necessary for him to coordinate with the well pump contractor to assure that an adequately sized well pump and tank are installed.

9.What do I look for in a contractor?

CERTIFICATION and EXPERIENCE! The contractor should be certified by the Interna¬tional Ground Source Heat Pump Association (IGSHPA) and should have demonstrated experience in installing GHP systems. Don’t be afraid to ask to see proof of certification and to ask the location of previous installations.

10.Can GHP systems be used in conjunction with hot water space heating?

Yes and no. Heat pumps are available from several manufact-urers that produce hot and chilled water rather than hot and cold air. These units can be connected to some types of hot water heating equipment. The limitation in the heating mode is temperature.

Conventional hot water radiators and base-board type elements are designed to operate at temperatures of 160oF and above (older systems as high as 200F).

Unitary heat pumps are limited to producing supply water temperatures of less than 120F. As a result, on a retrofit basis (a home with existing hot water radiator or baseboard), the prospects are not favorable.

The best hot water system to connect to a GHP are radiant floor (or hydronic radiant slab) systems.

This design, in which plastic tubing is installed in the floor slab as it is poured, operate at water temperatures typically much lower than radiator type systems.

In order to minimize the required water temperature, the home should be well insulated and use minimal floor coverings.

This type of system is more complex, in terms of equipment and controls than a standard water-to-air system and requires careful design.

In general, complete space cooling cannot be accomplished with a floor system since condensation would occur on the floor surface. As a result, this system generally must be coupled with some sort of fan coil unit to provide cooling and dehumidification.

11.Can snow melting be done?

Snow melting can be accomplished with GHPs; but, there are serious cost impacts on the residential side.

Due to the nature of snow melting, a separate system must be installed to serve the load.

This is due to its requirement for the circulation of an antifreeze fluid through the system, instead of the warm air supplied by water-to-air heat pumps.

Beyond this, since the requirement for snow melting coincides with the need for space heating, additional ground loop must be installed to serve the snow melting system.

Although GHPs produce heat less expensively than most other systems, because of the substantial quantities of heat required by snow melting systems, the annual cost remains high.

The high energy cost is a result of the way snow melt systems are operated. Most systems are allowed to “idle” at a low heat output during the winter season. This allows the paved surface to quickly come up to temperature when snow fall occurs.

The energy consumed by this idling operation, because of the number of hours over an entire season, is substantial.

Because of the thermal mass of the paved surface, simply turning the system on when snow fall occurs results in a long time lag (several hours to one day) between start up and snow melting. This results in incomplete snow removal and a “corduroy” effect on the surface.

The high energy cost is compounded by the need for high water temperatures to produce the necessary output required for adequate snow melting. These temperatures, in areas where heavy snow occurs, are far in excess of what would be produced by available unitary heat pump equipment.

The following evaluation of a snow melt system for a residence in Michigan points out some of the limitations.

“In your area, a snow melting system would be designed for an output of about 165 Btu/hr per square foot, under melting conditions. For a 12 ft wide 100 ft long driveway, this would amount to 198,000 Btu/hr or the equivalent of about a 20-ton heat pump. This is about six times the size heat pump required for the average house.

For snow melting conditions below 30oF and wind speeds above 5 mph, re¬quired water tempera-tures in the snow melt loop are in excess of 130oF. This is higher than the average heat pump can produce.

Because the snow melting system requires the circulation of hot water, a water¬to-water heat pump is required. Most homes with a geothermal heat pump use a water-to-air heat pump.

Snow melting requires a substantial amount of energy on an annual basis. In your area, a residential system would consume about 133,000 Btu/yr per square foot of driveway.

Supplying this from a geothermal heat pump, at a COP of 3.5, would require an electrical input of 11 kWh/sq ft of driveway. For a driveway of 1200 sq ft (100 ft x 12 ft), this would be about 13,200 kWh/yr or $924 per year at $0.07/kWh.”

Snow melting has been successfully incorporated into some commercial GHP systems serving gas stations/convenience store operations.

The advantage here is that the store contains a great deal of refrigeration equipment which continually produces waste heat used for the snow melting system.

The moral of the story is that snow melting can be done with geothermal heat pumps if money is no object. For most folks though, it’s much more economical to hire the neighborhood kid to shovel the driveway.

12. Can I heat my pool?

Pools can be heated with a geothermal heat pump and in very warm climates, this makes a good match with a space conditioning GCHP.

In cooling dominated climates, the space conditioning heat pump rejects much more heat to the ground than it absorbs from the ground.

As a result, there is the potential for a gradual increase in ground temperature to occur over a period of years, where a ground-coupled system is used. Removing this excess heat and delivering it to a swimming pool reduces (or eliminates) the problem.

Pool heating will require a separate heat pump for the pool. Beyond this, the heating capacity of the heat pump will likely be less than that of a typical gas-fired heater in the same application. This is a result of the fact that heat pumps cost about five times what
gas-fired pool heaters do per unit of heating capacity.

The smaller geothermal heat pump would not affect the ability to maintain pool temperature, but would result in a longer time required to bring the pool temperature from cold up to usable temperatures at the beginning of the season.

The pool geothermal heating unit would be of the water-to-water type rather than the water-to-air design used for home heating and air conditioning. The impact of the pool heating upon required loop length would depend upon the size of the pool and the amount of the year it is in operation.

13. I currently have a propane (or oil or gas) furnace and I am thinking about changing to a GHP. What should I be aware of?

First of all, there will be a major difference in the air temperature from the supply regis¬ters. Heat pumps, regardless of the type, produce lower temperature air than fossil fuel furnaces. Air-source heat pumps produce the coolest air 90 F to 95 F. GHPs produce air of 95 F to 103 F, a small but very noticeable improvement.

Another issue is the ductwork. If the house was not originally equipped for air condition¬ing, the ductwork may be undersized for the heat pump. Both central air conditioning and heat pumps require more air flow than fossil fuel furnaces. Be sure to have your contractor evaluate this issue. Undersized ductwork results in noise and lower system efficiency.

14. Are there any substantial improvements in efficiency on the horizon?

There are always improvements to be made in mechanical devices like heat pumps. This is not a reason to put off the installation of a GHP system, however. Most of the substantial efficiency gains have been made over the past 10 years.

Remaining improvements will likely be small in comparison to what has been achieved. As an example, the average performance of five manufacturer’s equipment found in the 1987 and current ARI Directo¬ries has shown an average of 41% improvement in EER and 27% improvement in COP.

15. I am planning a large home. Should I use one large unit or two smaller ones?

There are several reasons why it may be advisable to use two smaller units than one large one. The use of two or more small units is referred to in the HVAC trade as “zoning.” Generally a separate zone is established if one or more of the following criteria apply: the area has a specific use distinct from the rest of the home (mother-in-law’s apartment), the area is maintained at a distinct temperature (basement), a separate level of the home (2nd floor bedrooms).

An additional reason for using two systems is that the equipment of many manufacturers falls off in performance above four tons. As a result, the use of two 3-ton units is likely to yield a higher performance than a single 6- or 7-ton unit. This performance difference, however, is not sufficient to justify the additional cost of the 2-system design.

16. Is the system’s antifreeze a potential environmental problem?

In residential applications, the commonly used antifreeze solutions pose little to no environmental hazard. Each state regulates the types of antifreeze materials used in GHP systems.

The most commonly used ones are propylene glycol, and methanol. Propylene glycol is a non-toxic fluid which poses no hazards to the environment, humans or animals, and in fact, is used in food processing refrigeration.

Methanol (or alcohol) is potentially flammable, but not in the concentrations used in geothermal heating systems. It is similar to the antifreeze solution used in windshield washer systems.