Introductory Overview of Ground Source Heat Pump Technologies

Introductory Overview of Ground Source Heat Pump Technologies C. Guney Olgun Civil & Environmental Engineering Virginia Tech colgun@vt.edu Introduction to Ground Source Heat Pumps Virginia Cooperative ExtensionBioenergy Engineering Education Program Appomattox, VA April 13, 2015

Outline Background Energy demand Geothermal systems State of the GSHP industry Types of GSHP systems Closed loop systems Open loop systems

Learning Objectives Gain background on ground source heat pump (GSHP) systems Identify the basic principles of GSHP systems Identify different GSHP systems (closed loop vs. open loop, vertical vs. horizontal loop systems) Discuss advantages and disadvantages of GSHP systems Discuss cost related information on GSHP systems Learn about different applications of GSHP systems

U.S. Energy Flow Chart Lawrence Livermore National Lab (2009) Significant energy consumption in buildings mainly for heating and cooling

U.S. Geothermal Resources & Projects

U.S. Geothermal Resources WA OR CA NV MT ID UT WY CO ND SD NE MN IA MO WI IL MI IN OH WV NY VT PA ME AZ NM KS TX OK AR TN MS VA NC AL GA SC LA FL Temperatures above 212F Temperature above 100 o C (212 o F) Temperatures below 212F Temperature below 100 o C (212 o F) Area suitable for "Geothermal Foundations" (entire U.S.) Suitable for geothermal heat exchange (entire U.S.)

What is a Ground Source Heat Pump (GSHP)? GSHP is a electrically powered system that utilizes the relatively constant ground or groundwater temperatures to provide heating, cooling, and hot water Instead of burning fossil fuels to create heat like conventional systems, GSHPs move heat that already exists In heating mode, a GSHP moves heat from the ground or groundwater into the building In cooling mode, a GSHP moves heat from the building and deposits it into the ground or groundwater.

Ground Source Heat Pump Systems 1. Ground or groundwater heat exchanger 2. Heat pump 3. Interior heating/cooling distribution system 4. Domestic hot water heating (optional)

Ground Temperature Profile 0 Fall Spring 10 20 Winter Summer 30 Depth (ft) 40 50 60 70 Mean ground temperature Temperature ( F) 90 80 70 60 50 40 J F M A M Jn Jl A S O N D 59.2 F 90 80 70 60 50 40 80 Richmond, VA T mean = 59 F 35 40 45 50 55 60 65 70 75 80 85 Ground Temperature ( F) 30 30 Month

Ground Temperature Profile 0 Fall Spring 90 J F M A M Jn Jl A S O N D 10 Winter Summer 80 Ground Surface 20 Ground Temperature ( C) 70 60 50 40 30 5 ft 10 ft 50 ft 0 30 60 90 120 150 180 210 240 270 300 330 360 Depth (ft) 30 40 50 60 70 80 Richmond, VA T mean = 59 F 35 40 45 50 55 60 65 70 75 80 85 Ground Temperature ( F) Day of the Year Ground temperature fluctuations

Ground Temperature Profile 0 Fall Spring 10 Winter Summer 20 30 Depth (ft) 40 50 60 70 Williamsburg, VA T mean = 60 F 80 30 40 50 60 70 80 90 Mean ground temperature Ground Temperature ( F)

Ground Temperature Profile 0 Fall Spring 10 Winter Summer 20 Depth (ft) 30 40 50 60 Mean ground temperature 70 Baltimore, MD Tmean = 57 F 80 35 40 45 50 55 60 65 70 75 80 Ground Temperature ( F)

Ground Temperature Profile 0 Fall Spring 10 20 Winter Summer Depth (ft) 30 40 50 60 Mean ground temperature 70 Lawrence, KS T mean = 55 F 80 30 40 50 60 70 80 Ground Temperature ( F)

Ground Temperature Profile 0 Fall Spring 10 Winter Summer 20 30 Depth (ft) 40 50 60 Mean ground temperature 70 80 Houston, TX T mean = 72 F 40 50 60 70 80 90 100 Ground Temperature ( F)

Terminology Ground source heat pumps (GSHP) Geothermal heat pumps (GHP) Ground coupled heat pumps (GCHP) GeoExchange systems Earth energy systems

Ground Source Heat Pump Systems Primary circuit Secondary circuit Connecting lines Manifolds 0 10 20 30 Fall Winter Spring Summer Header block: Heat pump collector (for heating) distributor (for cooling) P P Depth (ft) 40 50 External power (electricity) 60 1 4 70 80 Richmond, VA T mean = 59 F 35 40 45 50 55 60 65 70 75 80 85 Ground Temperature ( F) Geothermal loops 3 4 Energy flux 4 4 (from the ground) Utilize the relatively constant temperature of the ground and use it for heating in the winter and cooling in the summer

GSHP Heating/Cooling Geothermal heat exchange systems provide ground-source energy for heating and cooling The use of ground-source systems for heating and cooling has increased exponentially especially in Europe Basic idea been around for long time make use of the heat energy stored in the ground; access this energy using heat exchangers buried in the ground (fluid-filled HDPE loops) In ideal conditions these systems can provide majority of required heating/cooling energy and significantly reduce costs and carbon footprint

Common Comments on GSHPs Advantages High efficiency results in lower energy consumption cost Lower maintenance cost Lower life cycle cost No outdoor equipment Greater occupant comfort All electric - can be powered by renewable energy Disadvantages First cost can be significantly higher than conventional systems Not all system types feasible in all locations Limited pool of qualified designers and installers in many locations

GSHP Domestic Shipments, 2002-2006 275,000 Total Rated Capacity Tons 250,000 225,000 200,000 175,000 150,000 125,000 100,000 2002 2003 2004 2005 2006 Source: EIA, Survey of Geothermal Heat Pump Shipments, 2006

GSHP Domestic Shipments, 2002-2006 120,000 Total Rated Capacity Tons 100,000 80,000 60,000 40,000 20,000 0 Residential Commercial (includes government) Industrial Source: EIA, Survey of Geothermal Heat Pump Shipments, 2006 Total Rated Capacity Tons 90,000 80,000 70,000 60,000 50,000 40,000 30,000 20,000 10,000 0 Midwest Northeast South West

GSHP : Closed Loop Systems Borehole Wells Horizontal Loops Helical Coils Energy Piles

Open Loop Systems Source eere.energy.gov

Barriers to wider GSHP Implementation Tend to have significantly higher first costs compared with conventional systems Generally longer paybacks when replacing natural gas heating systems Lack of awareness Lack of uniform standards design and installation accreditation has yet to receive nationally standardized accreditation Shortage of qualified designers and installers.

GSHP : Closed Loop Systems Borehole Wells Horizontal Loops Helical Coils Energy Piles

Borehole Wells 200 ft - 500 ft deep Small residential to large commercial Major cost is drilling and materials

Borehole Wells

Borehole Wells Design Considerations Spacing Grout Type Single U-bend or Double U-bend Ground properties: Temperature Thermal conductivity Thermal diffusivity Ground water Long-term effects

Helical Coils

Energy Piles

Vertical Ground Source Heat Pump Systems Piping is inserted to deep vertical boreholes. Boreholes are grouted to improve heat transfer and protect groundwater. Advantages Requires less land than other closed loop systems Requires smaller amounts of pipe and pumping energy Likely to yield the most efficient performance of closed loop systems Disadvantages Higher initial cost due to the drilling of boreholes Problems in some geological formations (an issue in parts of MA) Limited availability of experienced drillers and installers

GSHP : Closed Loop Systems Borehole Wells Horizontal Loops Helical Coils Energy Piles

Horizontal Loops 6-10 ft

Horizontal Loops Shallow ground water Spacing Pipe configuration: Straight Horizontal Slinky Vertical Slinky Soil properties: Temperature (seasonal variation) Thermal conductivity Thermal diffusivity

Horizontal Loops Recently built house in Blacksburg VA with a trench loop system

Horizontal Loops Horizontal loop systems within/beneath slabs

Horizontal Loops Energy slab (Messe U2 metro station, Vienna)

Horizontal Loops Deicing

Horizontal Ground Source Heat Pump Systems Placement of straight or slinky piping in shallow (6-8ft) horizontal trenches. Advantages Likely less expensive to install vertical closed loop Requires less specialized skill and equipment to install, so contractors are more widely available Disadvantages Need more space Ground temperature and thermal properties fluctuate with season, rainfall, and burial depth Lower efficiency

Open Loop Systems Source eere.energy.gov

Open Well Systems Water is pumped from bottom of well and re-injected at the top Heat exchange rate is enhanced by the pumping action Often utilized where little land is available or the bedrock is close to the surface During peak heating and cooling, the system can use a bleed cycle to control the column temperature Source: Orio, 2005. A Survey of Standing Column Well Installations in North America, ASHRAE Transactions. Information for Evaluating Geoexchange Applications, prepared for NYSERDA by the Geothermal Heat Pump Consortium.

Groundwater Heat Pump Systems Uses groundwater as heat sink and source. Water is pumped through the system, then discharged. Advantages Have the lowest installed cost, especially in larger applications Uses less space Well water contractors are widely available Long track record in large commercial applications Source: 2003 ASHRAE Applications Handbook Disadvantages Local water and environmental regulations may restrict use Limited water availability May need fouling precautions High pumping energy required if system poorly designed or water pulled from deep aquifer

Surface Water Heat Pump Systems The piping is anchored to the bottom of a nearby body of water Advantages Low cost due to reduced excavation costs Low maintenance Low operating costs Disadvantages Possible damage to piping in public lakes Significant temperature variation if lake is small/shallow

Hybrid Systems Use several different geothermal resources, or a combination of a geothermal resource with outdoor air (most often, a cooling tower) Particularly effective where cooling needs are significantly larger than heating needs. Cooling tower used to reject excess heat Main benefits: Reduces loop field size, and thus costs, by allowing for the ground loop to be undersized for the cool load, but sized for the smaller heating load Avoid increase in ground temperature due to seasonal load imbalances Source: Federal Energy Management Program, Assessment of hybrid geothermal heat pump systems, 2001

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