Geothermal Case Studies

Ground source heat pumps (GSHPs) provide a number of obvious benefits. The systems offer reliable heating and cooling while being energy efficient, quiet and virtually maintenance free. In addition to these more apparent benefits, the systems are also versatile. They provide a level of design freedom unmatched by other heating and cooling systems. Just ask Matt Keck, owner of Prairie Berry Winery located in the Black Hills of South Dakota.

Keck and a team from Skyline Engineering in Rapid City, S.D., designed a GSHP system that not only heats and cools Prairie Berry Winery but also controls the sensitive winemaking process. The system consists of two
water-to-water heat pumps that regulate wine production, two water-to-air heat pumps that serve the rest of the facility and radiant floor heating that helps dry the
production floors after washings and warms the outdoor patio.

“Winemaking is a fairly energy-intensive operation with large cooling requirements,” Keck said. “My thoughts were geared to minimizing the operating costs of the cooling plant.”

A chemical reaction known as fermentation is required for wine production. Fermentation uses yeast to convert sugar to alcohol and creates two byproducts: heat and carbon dioxide. Temperature plays a major role in the process because fermentation must proceed slowly. The higher the temperature, the faster fermentation will progress. During one of the final stages of winemaking, known as cold stabilization, the wine must remain at 30 F for two weeks. According to Keck, the loss of temperature control can ruin an entire batch of wine and generate a costly loss.

Keck said his wife is the winemaker. When asked what type of temperature control she needed for the wine-processing tanks she said the tanks should be individually controlled with the ability to be heated, cooled and sub-cooled.

“As a professional mechanical engineer with 10 years experience in the heating, ventilation and cooling industry, I had a firm knowledge of all the types of systems that were possible for our application,” Keck said.

The engineers designed a water-to-water system that produces three temperatures of water: 110 F, 45 F and 20 F. There are three storage tanks for each temperature of water and a control system that alternates the heat pumps to maintain each temperature. Each tank is covered by a jacket and valves are used to manually select which water temperature is fed into the jackets.

Prairie Berry not only produces wines from domestic fruits such as: apples, rhubarb, raspberries and strawberries but it also uses fruits native only to the Black Hills region. These include: chokecherries, buffaloberries, wild plums and wild grapes. Keck said most of the fruit arrives frozen so they have the ability
to ferment wine all year.

When the frozen fruit arrives it is put into a tank and heated. As fermentation begins and heat is released, the valve on the tank is switched to cool, removing the heat inside the tank and recycling it back into the GSHP system.

Keck said one of his favorite aspects of the design is its ability to provide free process cooling in the winter.
The winery’s system employs a manual crossover that uses geothermal condenser water as a replacement
for the 45 F water that would otherwise have to be produced by the system. As part of a traditional GSHP system, a desuperheater can provide a similar benefit by recycling waste heat to produce hot water in the summer.The winery’s condenser water runs at about 35 to 40 F. The heat of fermentation is then added to the condenser water and extracted for use in the tasting room’s water-to-air pumps.

“The system performance is certainly improved by this free cooling,” Keck said. “In theory, we are able to operate a closed loop scenario without the need for the loop field.”

The design also features redundant loop pumps that increase the reliability of the system. Three separate manifolds operate with seven wells on each. If damage occurs to one of the manifolds, it can be isolated and the winemaking process can continue with reduced capacity using the two remaining manifolds. There are also provisions for the addition of a back-up generator, which is a great defense against heavy snowfalls that could cause power outages and impede the winemaking process.

“It is difficult and costly to obtain the same level of redundancy with a cooling tower or dry cooler,” Keck said. “In addition, these devices are subject to failure and vandalism.”

Groundbreaking for the winery took place in November 2003. The 18-ton system uses Florida Heat Pumps, which were installed by Action Mechanical of South Dakota. The installation required 20 wells dug to a depth of 200 feet. Black Hills Power, a local utility, offered incentives to the winery for the installation and use of a GSHP system.

“The intent of our customer incentives for geothermal systems is to encourage the installation of energy efficient electrical equipment, help offset the cost of loop fields and better use our generating capacity,” said Jim Keck of Black Hills Power.

Black Hills Power also bills the winery based on an energy storage rate. This rate was created for customers who operate systems that promote off-peak energy use. Off-peak times are defined as overnight, early morning, weekends and major holidays. A GSHP system makes better use of generating capacity because it reduces the utility’s on-peak energy demand, J. Keck said. Typical energy storage applications include: ice storage, heat storage and pumped water storage. Energy storage equipment is metered separately from a facility’s general electric loads.

“Although geothermal systems use both on-peak and off-peak energy, Black Hills Power qualifies them for our energy storage rate,” J. Keck said. “We do not penalize them for on-peak energy use because of their benefits to Black Hills Power and the fact that these applications are energy storage in nature.”

Based on billing records, Black Hills Power approximates the winery’s first year operating costs were $0.76 per square foot. Compared to the cost of propane, the area’s only heating competitor, the winery has saved over $5,000 in its first year by installing a GSHP system. M. Keck estimates the total cost of the installation to be $30,000.

These figures project that the system will begin payback in as soon as six years. M. Keck also said the GSHP system runs exceptionally well with little supervision.

“The operational cost savings alone are a great benefit and our electricity bill is amazingly low,” M. Keck said. “Additionally, the system is quiet, there are no outdoor units and maintenance is minimal.”

The winery’s tasting room opened in June 2004 and wine production began in November 2004. It is a 13,000 square foot facility and is open six days a week for wine tasting. Tours of the production areas are offered only during special events or on a pre-arranged basis, however, part of the production area can be seen through large windows in the tasting room. M. Keck said the winery is also currently working on a display explaining how the facility utilizes geothermal heating and cooling.

The winery is located near popular South Dakota tourist attractions such as Mount Rushmore and the Crazy Horse Memorial. M. Keck says the winery sees most of its visitors during summer vacation and the winter holiday season. So to witness true energy efficiency and experience the benefits of geothermal versatility, visit Prairie Berry Winery in the Black Hills of South Dakota.

Volume 2, Number 4 Geo Outlook
©2006 International Ground Source Heat Pump Association