How To Use Geothermal Heat Pumps To Save Running Costs in LEED v.4
Above: Coils for a ground source heat pump in a trench. Right: Fitting the heating/cooling system indoors.
Understanding how LEED credits apply to the geothermal industry, how to pursue points using geothermal technologies, and how the changes in v4 fit into the geothermal energy sector value chain can unlock business value for manufacturers, design firms and service providers.
What is changing?
There have been positive market transformations in the energy efficiency sector over the past 5 years. Additionally, LEED v4 system goals have expanded beyond energy consumption and emphasize the enhancement of human health, sustainable material cycles, and more. For these reasons, there has been a redistribution of points in the rating system, as well as in the credit categories.
- Total points for the Energy & Atmosphere category of LEED BD+C have decreased from 35 to 33
- The Optimize energy performance credit has decreased from 19 to 18 possible points
- The Renewable energy production credit has decreased from 7 to 3 possible points
What is staying the same?
- LEED v4 is comprised of the same number of points as v2009, and point thresholds for certification levels have stayed the same
- Ground source heat pumps are still eligible to apply for the Optimize energy performance credit
- Direct use geothermal plants are still eligible to apply for the Renewable energy production credit.
How does LEED v4 benefit the geothermal industry?
LEED v4 has updated the reference standard for energy performance to ASHRAE 90.1 2010. See Figure 1 for a table of changes between the 2007 and 2010 editions. ASHRAE 90.1-2010's mandatory requirements require increased efficiencies for all chiller types, heat pumps, and economizers. Also, water-to-water heat pumps and variable refrigerant flow units are now covered in the standard.
Summary of Changes between ASHRAE 90.1-2007 and 2010 (from LEED v4 Reference Guide).
By increasing efficiency requirements for a variety of HVAC systems, and including new types of technology in the standard, project teams will be encouraged to learn more about innovative HVAC systems, and will be more likely to consider high performance geothermal HVAC technologies like ground source heat pumps.
Which credits provide the most value to the geothermal industry?
The most pertinent credits to focus on in LEED v4 are the Optimize energy performance (Oep) credit and the Renewable energy production (Rep) credit. The Optimize energy performance (Oep) credit accounts for 18% of the possible points in LEED v4, and the Renewable energy production (Rep) credit accounts for 3%.
Note: Statements made about possible point attainment in this brief are generalizations and should not be taken as guarantees, as actual results will vary depending on fuel source, building characteristics, internal loads, site location, and local climate.
Pursuing points in the Optimize energy performance (Oep) credit
Utilizing ground source heat pumps (GSHPs) as part of the HVAC system on a project is an effective way to receive a substantial portion of the points in the Oep credit. This is a result of the poor efficiencies of the baseline HVAC system types in ASHRAE 90.1-2010 (see Figure 2). These types are used as baseline HVAC systems to compare against when generating energy models for a proposed project seeking LEED certification. The percent by which the project's chosen HVAC systems outperform the baseline determines the amount of points a project can receive for the credit.
Above: Tables of Baseline HVAC Types from ASHRAE 90.1-2010.
There are 10 baseline systems described in the standard, and depending on the predominant system and any other systems used for backup capacity, each has a different system efficiency. In most, if not all cases, a GSHP would be more efficient, and provide energy savings that could lead to receiving points in the Oep credit. The amount of points the project could attain depends on the selected baseline system[1], as well as how well balanced the loop is, whether the air supply is constant volume or variable, whether it is possible to operate some spaces in heating mode and others in cooling mode at the same time, and so on.
It is complex to attempt to generalize the overall efficiencies of different HVAC systems, and electric system efficiencies change depending on outside air temperature. But, if a typical 100,000+ square foot office building project in a climate with high heating loads[2] is considered, the baseline system types, from best to worst efficiency could be:
Based on past certifications, generally, projects using a GSHP stand to attain most, if not all of the points in the Oep credit if electric resistance is the sole baseline heating source (and there is no backup fossil fuel boiler), and can get around half of the points if a fossil fuel baseline HVAC system is selected.
Pursuing points in the Renewable energy production (Rep) credit
Note: only projects with a direct use geothermal system are eligible to apply for this credit; projects using heat pumps or any system with a vapor compression cycle must apply for points in the Oep credit described above.
According to the Oregon Institute of Technology's Geo-Heat Center, there are nearly 12,000 geothermal wells and springs (above 68 °F) in the western United States. Just over 400 communities are collocated to a geothermal resource (with temperatures above 122 °F).
Projects with direct use projects can attain up to 3 points in LEED v4, by either utilizing steam or hot water from an on-site geothermal source to either use for space heating or power generation. Projects with off-site geothermal resources that directly use hot water or steam to feed into a district heating system can also get points in this credit through the community energy systems addition in v4.
How does LEED v4 offer geothermal industry professionals a competitive advantage?
Geothermal heat pumps offer a highly efficient alternative to conventional HVAC systems. Geothermal industry participants should take note of the large number of points a GSHP system can qualify to receive, and market their products and services relating to these technologies accordingly.
Direct use geothermal systems are not very common in the United States, but they provide advocates of geothermal combined heat and power plants and district heating systems with another avenue to receive points in LEED. Encouraging project teams to assess possible resources in their locale and pursuing a direct use system may lead to increased market penetration and new business opportunities.
[1] If a project uses both electric and fossil fuel HVAC types, the baseline is determined as whichever system services the larger floor area: at the bottom of Table G3.1.1A in Figure 2, it says that "Where attributes make a building eligible for more than one baseline system type, use the predominant condition to determine the system type for entire building". If more than 20,000 square feet of the project utilizes a supplemental fossil fuel system, the project must select a "fossil/electric hybrid" system baseline type.
[3] When temperatures drop below 40 °F, a heat pump must utilize the backup electric resistance heating system, which reduces the overall system efficiency. As temperatures get lower, the combined efficiencies decrease significantly, and when temperatures go below 17 °F, the baseline must be modeled as completely supplied via the electric resistance system. GSHP loop efficiencies also drop as the ground water temperatures drop, but the efficiencies significantly exceed those of the air-source heat pumps in the baseline systems as the outside air temperatures drop further and further below 40 °F. At outside air temperatures of 17 °F, the ground source heat pumps can use 33% or less than the energy required to operate electric resistance heating at the same temperature.
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- How To Retrofit the Most Efficient Lighting and LEED Approval
- Water Source Heat Pumps and District Heating
- Renewable Energy Toolkit for Enterprises
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Post authored by Gretchen Heberling