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Wisconsin Perspective™

A PUBLICATION FOR WISCONSIN/ U.P. PLUMBING-HVAC-MECHANICAL AND RELATED INDUSTRIES

Report from KBIS 2010Page 8

Page 16

The key to cost-effective firestopping

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Green Perspective™

Fourth in a ser ies by Ron MacKinnon

Geothermal — the importance of designThe goal of this article is to provide insight into and anunderstanding of the importance of design to any HVAC sys-

tem, but more importantly, to geothermal systems.

The U.S. Environmental Protection Agency has concluded

that well-designed and properly installed high-efficiency geo-

exchange heat pump systems produce less environmental

harm than any other alternative space-conditioning technolo-

gy currently available.

Geo-exchange systems are the most efficient technology

available, with the lowest CO2 emissions for minimum green-

house warming impact. Overall, the EPA found geo-exchange

heating and cooling systems to have the lowest environmental

cost of all technologies analyzed—including air-source heat

pumps and natural gas furnaces.

Numerous studies have shown that heat pumps are often

sized too large. For maximum efficiency, heating and cooling

loads should be carefully determined using accepted proce-

dures such as the Air Conditioning Contractors Association’s

Manual J. If a system is designed to -15°, and we know that we

spend less than 10 days at that temperature annually, it can be

easily determined that most systems are oversized, not just

geothermal systems.

The design of a geothermal system must always start with

a proper heat/cool load calculation. This is the only way a sys-

tem can be sized properly and offer the cost-of-operation sav-

ings the system is capable of. Whether it is new construction

or a retrofit application, I can’t stress enough the importance

of the load calculations.

Once the loads are determined,many manufacturers of geothermal

systems like, Climatemaster, offer

geothermal design programs like

Geodesigner. These programs in-

corporate all the data necessary to

properly design and size a geother-

mal system. Such as the following:

• Climate data

• Soil types and their conductivity

• Loop field configurations

• Equipment selection

• Utility costs

• Sizing comparisons

• Systems cost of operation for comparison

There is a lot to consider when designing a geothermal sys-

tem. The orientation of the loop field: Will it be horizontal or

vertical? What type of horizontal loop field: slinky or racetrack?

What depth will vertical wells be? What type of ground or soil

will the loop field be installed in? Different soil types vary in

how much the soil will give up (heat of extraction heating

mode) and how much it will accept (heat of rejection in cooling

mode). This is very important, and rule of thumb calculations

or assumptions should be avoided. What size PE pipe should

be used? The larger the pipe diameter, the more flow can be

accomplished, so careful consideration must be employed

when selecting the proper pipe size based on the flow rate

needed to support the geothermal system.

(continued on page 34) 

March-April

2010

March-April 2010 33

Ron MacKinnon 

geothermal/hydronic 

product specialist 

A Renewable Energy Section for

Plumbing, HVAC, Mechanical

and Related Industries

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(continued from page 33) 

Closed-loop geothermal systems require a flow rate of 3

gpm per ton, so a 4-ton system will require a flow rate of 12

gpm to maximize its capacity. To accomplish this, a loop field

must be sized correctly, but just as importantly, the pump flow

station must be sized to provide the correct flow. I can’t countthe number of situations I have encountered that have either

to much flow or, worse yet, not enough. Without accurate flow

measurement, the commissioning of a geothermal system is a

guess at best.

The rule of thumb for sizing pump stations, which are avail-

able in a single-pump or double-pump configuration, is that a

3-ton system and below will require a single-pump station and

4-ton and up requires a double-pump station.This may be fine

for estimating projects, but the reality of it is that in some cases

a single will work on a 4-ton and a double is sometimes need-

ed on a 3-ton system.To ensure that adequate flow is attained,

the following must happen: A loop field pressure drop calcula-

tion needs to be completed for each loop field. This calculation

will model the loop field and provide the head that needs to be

overcome. Further it will provide the amount of fluid in the sys-

tem and determine the amount of anti-freeze required to get

the proper freeze protection.

In short, you total up the supply and return piping from the

header into the flow station and then add in the longest loop.

This calculation also incorporates the head produced by the

equipment’s heat exchanger as well.The key to this calculation

is the freeze protection used. Ethanol and glycol freeze-pro-

tection fluids are most commonly used in northern climates for

freeze protection. Typically you will see freeze protection

between 10° to 15°F. This is usually a 25% antifreeze-to-water

mix. Ethanol is much easier to pump than glycol, especially

when glycol gets colder (below 40°F). So you can have a par-

ticular loop field using ethanol, and a single-pump flow station

will work correctly, but change the freeze protection to glycol,

and it won’t. So in this case a double-pump flow station would

be required to ensure adequate flow through the system.

Once you have determined the load, and designed and

sized the geothermal system and the associated loop field, the

next part of the system is designed: the distribution system.

The distribution system could be either a properly engineered

sheet metal duct system, a radiant infloor system, fan coil, or

a low-temperature baseboard system. No matter the distribu-

tion system, careful attention must be paid to its design. You

may have a properly designed and sized loop field and geo-

thermal system, but if the distribution system is not designed

in concert the overall performance, the system will be nega-

tively affected. The result is a system that will not perform effi-ciently. This results in customer callbacks and numerous hours

spent troubleshooting the equipment and loop field, overlook-

ing the distribution system which, in some cases, is the actual

cause of the callback.

Geothermal systems are relatively low-tech systems. They

are often perceived to be very complicated, but they are not,

however, proper training and education is a must since geo-

thermal systems are unique in detail. With their increasing

popularity, I have seen the rush by companies to get involved

with geothermal systems as an addition to their offerings. A

word of caution on that: It is imperative that anyone getting into

the geothermal market make sure they receive the proper

training and, just as importantly, use that knowledge to ensure

successful installations. It is not only good for the contractor,

but is good for the customer as well. Remember that they are

the ones buying the technology.

Geothermal manufacturers and distributors like Climate-

master and Milwaukee Stove offer training in all areas of geo-

thermal: design, installation, service, and sales, to name a few.

They understand a properly designed system is imperative to

the growth of this industry. They are making the investment to

ensure it.

So, if you’re in the market for a geothermal system for your

home or commercial project, I recommend that you do your

homework on the front end. I would also recommend that you

seek out contractors who are not only qualified but have expe-

rience designing and installing these systems. Ask: How many

systems have you installed? What training have you had? And

ask for at least three references. A great place to start is the

Wisconsin Geothermal Association. Here you will find the

most experienced contractors available in your area.

In my next article we will discuss the economics of geother-

mal systems and what they actually cost to install. We will also

be discussing cost of operation and determine the actual pay-

back period once and for all. •

featureGreen Perspective

34 March-April 2010

Permission to reprint this article regarding geothermal systems was provided courtesy of  Wisconsin Perspective™ magazine,

a publication for Wisconsin and U.P. plumbing, mechanical, and HVAC-R-related industries. ©2010  Wisconsin Perspective.