Geothermal HVAC Systems

- The Basics and Applications (Draft)

© George Hu, P.E., LEED AP Air Water Energy Engineers, Inc.

Updated 11/27/2012

The Geothermal Basics

Geothermal Map of the U.S.A.:

Map source: Geo-heat Center, Oregon Institute of Technology

Terminology: “Geothermal” vs. “GSHP”

Geothermal Resources Classification per DOE High temperature geothermal resources: Underground reservoirs of steam, hot water and dry hot rocks (e.g., electricity generation via steam turbines) Moderate-to-low temperature geothermal resources: Direct use applications such as for space heating Lower temperature, shallow ground geothermal resources: Used by geothermal heat pumps for space heating and cooling

Temperature > 212 F

Temperature < 212 F

On-site Renewable Energy Classification per USGBC Deep-earth water or steam sources: Geothermal energy systems using deep-earth water or steam sources (but not vapor compression systems for heat transfer). These types of systems are eligible for renewable energy credits for LEED. Examples include Geothermal Heating Systems, Geothermal Electric Systems. Geoexchange / Ground Source Heat Pump / Geothermal Heat Pump systems: Systems that use vapor compression cycles for heat transfer and do not obtain significant quantities of deep earth heat. These types of systems are ineligible for on-site renewable energy credits for LEED.

Ground Source Heat Pump Systems (aka Geothermal Heat Pump Systems) for Building HVAC

Water-to-Air Ground Source Heat Pump:

Water-to-Water Ground Source Heat Pump:

(Refrigerant) Vapor Compression Cycles

(Refrigerant) Vapor Compression Cycles

System Types by Ground Loop Construction

Horizontal Closed Loop System:

Vertical Closed Loop System:

Ground is heat storage device: • Heat rejected to ground in cooling season • Heat extracted from ground in heating season

Buried HDPE pipes

Pump circulating water / glycol in ground loop

Ground is heat storage device: • Heat rejected to ground in cooling season • Heat extracted from ground in heating season

HDPE U-tubes in vertical boreholes

Pump circulating water / glycol in ground loop

Standing Column Well System:

Lake Source Closed Loop:

Lake Source Open Loop:

Open Loop (no glycol)

Well Pump

Emergency bleed to prevent heat pump freezing or loop temperature too high

Coil or heat exchanger isolates heat transfer

fluid and source water

Lake, River or Other Water Body

Lake, River or Other Water Body

Direct use of source water

Ground Water Temperatures in the U.S.A.

Example underground Temperatures:

Boston: 50 oF Philadelphia: 55 oF Miami: 78 oF

Constant underground temperatures: - Warm during heating season; - Cool during cooling season - High energy efficiency for heat

pumps due to the physics of heat transfer

Data source: ASHRAE “Design of Geothermal Systems for Commercial and Institutional Buildings”, 1997

High Energy Efficiency of Geothermal Heat Pump Systems

Heat from the Ground

For example, in heating application, for a heat pump with COP = 4.0, for every BTU of heat delivered to space, ¼, or 0.25 BTU comes from electricity, the other 3/4 BTU comes from the ground. The water pump also consumes certain amount of electricity, but compared with the heat delivered to the space, that amount of electricity is very small, therefore not substantially affecting the overall system COP. (COP = Coefficient of Performance = heat output / electricity input) With oil or gas-fired heating system, for every BTU of heat to be delivered to the space, it requires 1 BTU of oil or gas to be burnt. Considering the fact that the fuel burning device (e.g., boiler) is not 100% efficient, it actually requires more than 1 BTU of fuel to be burnt (for boiler efficiency of 85%, it requires 1.18 BTU to be burnt). During cooling seasons, the geothermal heat pump system is also more energy efficient than conventional air-cooled systems, because the ground is cooler than the air, making it easier for the heat to be ejected to the ground than to the air. Efficiency from Heat Recovery

Heating Cooling Cooling

Cooling Heating

Rejected heat from cooling units gets utilized by heating units in the same ground loop

Geothermal Heat Pump System Applications

Heating, Ventilating and Air-Conditioning (HVAC)

HVAC with geothermal heat pump systems can be applied to all geographic areas in the U.S. However, application to certain climate areas where either heating or cooling is dominant require careful consideration of the specific building and its requirement. In heating or cooling dominant climate areas, ground heat imbalance could be a problem, but it depends on the specific building project and its requirement. Proper systems could be engineered to address ground heat imbalance concerns or even take advantage of it to the project’s benefit. Contact your geothermal engineer to assess the suitability of geothermal for your project. Domestic Hot Water Heating

The high energy efficiency of geothermal heat pump systems can be taken advantage to produce domestic hot water. For residential and light commercial applications, the temperature of hot water produced by residential type geothermal heat pumps is usually limited to 120 oF, just high enough to meet most residential domestic use. With new technology available today, large commercial HVAC equipment manufacturers are making geothermal heat pump products that are capable of producing hot water temperatures up to 170 to 180 oF, suitable for large commercial projects. Snow-melting

Snow melting is an energy intensive activity, which makes geothermal heat pump systems appealing due to their high energy efficiency. Snow melting systems may be a requirement in places such as emergency access areas of hospitals, airports and other critical commercial or industrial facilities. Snow melting systems also found their use in residential driveways especially in luxury houses. District Heating and Cooling Sources for Campuses or Group of Buildings

Geothermal Heat Pump Systems are increasingly being used as district heating and cooling energy sources for campuses and group of buildings, due to their high energy efficiency and reduced environmental impact such as reduced greenhouse gas emissions. Sometimes these district energy systems are built to replace existing “dirty” coal-fired energy plants in university campuses. Geothermal heat pump systems have also been successfully built for large residential projects that involve multiple houses or apartment buildings. Wide Variety of Building Types Potential Candidates for Geothermal Systems

Geothermal heat pump systems do not use any fuel but electricity, which almost any building project has access to. In theory, any building which needs heating and/or cooling can utilize geothermal heat pump systems. Practically, geothermal application may be limited by available land area to lay out horizontal ground loops or to drill the required number of vertical boreholes; or, it may be limited by the lack of water rights or strict environmental regulations if it is a lake or river type system in question. Other practical concerns include higher upfront costs, which involves the calculations of economics or return of investment period to verify geothermal feasibility.

Because of geothermal systems’ high energy efficiency and the fact that they don’t require boilers and chillers / cooling towers, and the fact that the ground loop, once built, is invisible, there are certain types of building projects are particularly suited for geothermal systems, such as: Renovation of historical buildings

• Lack of room to install major mechanical equipment such as chillers and cooling towers • Lack of room to run major ductwork and other mechanical components • Aesthetics is a primary concern

Building projects that have high energy performance goals and/or high LEED certification goals

• High energy efficiency of geothermal system helps to achieve the goal Buildings that target for net-zero energy performance

• High energy consumption reduction by geothermal system make net-zero energy goal easier to achieve

Buildings that are highly energy intensive (such as hospitals, research labs etc.)

• The economics are easier to work out to favor geothermal systems when the building is highly energy intensive – payback time would be shorter

Buildings that lack access to natural gas

• It’s an opportunity to go with the clean, high energy efficiency geothermal system Buildings that is close to available water bodies such as a river or a lake

• This is particularly true for many existing mill buildings which used to rely on hydro power from the rivers to drive the machines inside the buildings

Buildings owned by institutions

• Institutional buildings are usually owned by the same owner for long period of time, the owner reap the operational savings from the geothermal systems

Buildings that want to project image of sustainability conscientiousness

• The building itself could be a good educational tool for its occupants regarding sustainability. Having a geothermal system enhances that image

There are many factors to consider for potential geothermal systems for a particular building project. That is especially true for existing buildings. For suitability of geothermal for your specific project, solicit advice from your geothermal HVAC engineer.

A Glance of Reported Geothermal HVAC Projects

Project Size Location Geothermal

System Type

Energy

Savings

Carbon

Reduct

ion

Payback

Time

Comments

Eureka

Lodge

Retrofit

(2008)

28-room, 11,000 SF

Eureka, CO Open Loop $1,650 /month N/A N/A Geothermal enabled building/business to operate year-round, not limited by unavailability of propane during snow season

King’s Mill

Hospital

(2011)

920-bed, 1.4m SF

Mansfield, England

Lake Source Closed Loop

£126,500 /Yr 2,078 Tons /Yr

N/A

Cerom Grain

Research

Center

(2009)

25,600 SF Main Bldg. + (3) 1,700 SF Greenhouses

Montreal, Canada

Vertical Closed Loop

$63,000 / Yr 347 Tons / Yr

4.3 Years

Chinese

National

Stadium (The

Bird Nest)

(2008)

91,000-seat Beijing, China

Vertical Closed Loop

N/A N/A N/A Geothermal heating & cooling for athletic suites, media rooms, underground venues

Liberty

Island Retail

Pavilion

(2010)

7,000 SF Liberty Island, NY

Standing Column Well

N/A N/A N/A Fuel oil expensive on the island; Unsightly mechanical equipment not desired due to location

Springhill

Suites Hotel

(2008)

80,145 SF Pensacola Beach, FL

Vertical Closed Loop; Hybrid System

Energy intensity 43% lower than comparison w/ conventional system

N/A Payback not in question – system cost less than conventional system

Mistissini

Community

Center

(2009)

74,809 SF North Quebec, Canada

Vertical Closed Loop

$153,600 /Yr N/A 4.6 Years Facility has ice arena that requires simultaneous heating & cooling

NewBridge

on the

Charles

Hebrew

Senior Life

Community

(2009)

1m SF Dedham, MA

Vertical Closed Loop

$325,000 / Yr 8,000 Tons / Yr

7.5 Years

Whitmore

Lake High

School

(2006)

150,000 SF Whitmore Lake, MI

Horizontal Loop + Lake Source Closed Loop

35% savings N/A N/A

Ball State

University

5.8m SF, 40+ buildings

Muncie, IN Vertical Closed Loop

$2m / Yr N/A 8.8 Years Convert entire campus to geothermal, 1st phase started in 2009.

West Chester

University

1.8m SF West Chester, PA

Vertical Closed Loop

N/A N/A N/A

Private

Residence

(2009)

15,000 SF Rye, NH Vertical Closed Loop

70% + savings for heating; 40% savings for cooling

N/A N/A

Driveway

Snow-melting

System

(2010)

~7,000 SF driveway

Rye, NH Vertical Closed Loop

66 – 88% savings compared with 2008 & 2009

N/A N/A