Ground-Source Variable Refrigerant Flow Heat Pumps: a Solution for Affordable Housing, Assisted Living, Hotels and Dorms

Energy Efficiency Factsheet: Ground-Source Variable Refrigerant Flow Heat Pumps • Page 1

Ground-Source Variable Refrigerant Flow Heat Pumps: A Solution for Affordable Housing, Assisted Living, Hotels and Dorms

By Marcia Karr, P.E. Energy Engineer, Washington State University Extension Energy Program

In recent years, the decreasing to use in other zones (in buildings standards. AHRI tests equip- costs and increasing quality of where some zones are in heating ment under identical laboratory variable refrigerant flow (VRF) mode while others are in cooling conditions to determine its rating. equipment have led to efficiencies mode). This rating allows for apples-to- comparable to – and even exceed- apples comparisons of efficiency ing – the efficiency of standard A ground-source VRF heat pump among different manufacturers. ground-source heat pump (GSHP) system combines the advantages It turns out, however, that the systems. Because of this, the cost- of both technologies into one performance of air-to-air systems effectiveness of installing ground- system, making it one of the most in real world conditions, where source heating, ventilating, and air efficient HVAC systems available the equipment is exposed to very conditioning (HVAC) systems has for many applications. By using hot and very cold conditions, is been called into question. ground water loops, multi-speed often inferior to performance in fans and variable speed compres- lab conditions. To compensate The advantages of GSHPs sors, ground-source VRF heat for decreased performance in (sometimes called geothermal pump systems achieve savings over extreme conditions, equipment is heat pumps) are that they either GSHP or VRF on their own. often specified to be over-sized. tap a large reservoir of nearly If ambient conditions were more constant-temperature heat (the What is a Ground- moderate and more predictable, ground) and they use water as the this over-sizing would not be heat-exchange fluid, which is more Source Heat Pump? necessary. A typical heat pump heating efficient than using air. However, and cooling system is called an VRF technology, even with air-to- One way to achieve relatively air-to-air heat pump because it air heat exchangers, can meet or constant ambient conditions is to exchanges heat with outside air exceed the efficiencies of GSHPs by bury pipes underground, where in order to provide heating or using multi-speed fans and variable the temperature is relatively con- cooling. These heat pumps are speed compressors. In addition, stant year round. Because heat is rated based on American Heating VRF technology enables recovery exchanged with the ground rather and Refrigeration Institute (AHRI) of heat or cooling from one zone than the outside air, GSHPs remain Energy Efficiency Factsheet: Ground-Source Variable Refrigerant Flow Heat Pumps • Page 2 a very efficient source of heating efficiently than air, the system configurations: slinky or and cooling all year. gains additional efficiency by using straight horizontal trenches water as the heat exchange fluid. (Figure 1), vertical wells The GSHPs typically use the (Figure 2) and pond/lake refrigerants R-22 or R410A, which The piping system can be install- source (Figure 3). are well-suited to efficiently draw ed in one of four common • Open loop system, which heat from or reject heat to water configurations: requires an underground in this temperature range. Because • Closed loop systems, well (Figure 4). water transfers heat much more which consist of three

Figure 1. Horizontal trenches Figure 2. Vertical wells

Figure 3. Pond source Figure 4. Open well Energy Efficiency Factsheet: Ground-Source Variable Refrigerant Flow Heat Pumps • Page 3

Things to consider: • Minimal losses from ducts (EER) is described as “not so good 1. Pipe length depends on since most or all of the at indicating energy (kWh) savings a number of factors, but ductwork is eliminated. potential.” As noted on slide 5, for estimating purposes a Eliminating ducts may IEER “may be a better indicator of rule of thumb is about 400 also allow buildings to be energy usage.” lineal feet per 400 square designed with lower floor- feet of building. The slinky to-floor heights, reducing VRF systems have heat exchanger design shown in Figure construction costs. units located outdoors that are 1 requires an area for connected to one or more indoor trenches that is about twice These features, as shown in Figure units. In some conditions, one the area of the building. 5, make VRF more efficient than or more units may be in heating 2. “Construction hygiene” is most other HVAC and water mode at the same time that others critical. The piping must heating technologies in many are in cooling mode. This feature be protected from dirt, applications. The American Society allows heat rejected from rooms critters and other sources of Heating, Refrigerating and Air that are in cooling mode to be of contamination. Conditioning Engineers (ASHRAE) used by other rooms that are in 3. The horizontal piping and AHRI have developed a new heating mode. should be 5-10 feet deep, efficiency test standard – Standard depending on frost level. 1230 – to capture these features. The deeper the pipe, the The new standard is the Integrated VRF Benefits Some of the benefits of VRF more stable the tempera- Energy Efficiency Ratio (IEER), systems are: ture; the more stable the which was developed to more • Energy savings due to temperature, the more accurately reflect the efficiency of better part-load efficiencies efficient the system. VRF systems. As shown on slide 4 and reducing or eliminat- 4. Heat pump systems can in this ICF International presenta- ing duct losses, when provide pre-heating for tion on EER and IEER Ratings in compared to standard potable hot water with a HVAC Program Implementation air-to-air heat pumps. desuperheater when the (http://www.cee1.org/cee/mtg/06- • Smaller mechanical space heat pump is in cooling 10mtg/files/ComHVAC_ICF_Odell. requirements, both interior mode. pdf), the energy efficiency ratio

What is Variable Figure 5. Refrigerant Flow? A typical VRF application VRF equipment has the following features that make it a very efficient HVAC system: • Multi-speed fans on the indoor and outdoor units rather than single-speed fans. • Linear expansion valve rather than open/close. • Variable speed compressor. • Internal/external heat recovery between zones. Heat rejected from one zone can be used in another part of the building rather than being rejected to the outside. Energy Efficiency Factsheet: Ground-Source Variable Refrigerant Flow Heat Pumps • Page 4

and exterior. • Design flexibility with the Figure 6. variety of indoor air VRF market share in various markets handler options. • Easier retrofits where Window Japan running ductwork is an 90% Unitary 7.2M Systems Chillers issue, such as an older Moveable building that lacks duct- Ductless work or where the current ductwork is undersized. China USA 86% 3% • In retrofit applications, 16.7M Systems 0.2M Systems existing ductwork can be used for ventilation air. Ductless is a small percent of the U.S. HVAC market but current • Greater rentable space Europe building and energy usage due to smaller mechanical 81% trends indicate a large growth opportunity. rooms. 7.6M Systems • Lower construction costs due to less space required between floors for ductwork. The modeling software algorithms Applying Ground- • Relatively lighter weight, have resulted in conservative Source VRF Heat Pumps minimizing structural energy savings. Using Energy requirements. Star’s Portfolio Manager (http:// in the Real World www.energystar.gov/index. The Little Deschutes Lodge The VRF technology is not new; in cfm?c=evaluate_performance. (http://www.discoveryparklodge. fact, it is the technology of choice bus_portfoliomanager), many com/littledeschuteslodge), an in Japan, China and Europe, as VRF buildings have come in with affordable housing project for depicted in Figure 6. energy use index (EUI) better than seniors in La Pine, Oregon, has the model results. a ground-source VRF heat pump The term “ductless” in this chart system and the facility is nearly is synonymous with VRF. However, VRF now includes many styles of Figure 7. equipment, including wall- Percent theoretical savings over air-source heat pump mounted ductless, above ceiling ducted, cassettes, floor mount Portland and more. Seattle Figure 7. What Are Potential Kansas CityPercent theoretical savings Dallasover air-source heat pump Energy Savings of a Lincoln Ground-Source VRF Fargo Heat Pump System? Salt Lake To compare the energy use of Denver various HVAC systems, a 25,000 square foot single-story assisted Phoenix living building was modeled for 10 Billings cities using using Energy Pro building modeling software. The energy 0% 10% 20% 30% 40% 50% used per system type and per city is noted in Figure 7 and Table 1 Ground-Source VRF Savings vs. HP VRF Savings vs. HP GSHP Savings vs. HP (see next page). Energy Efficiency Factsheet: Ground-Source Variable Refrigerant Flow Heat Pumps • Page 5

Table 1. Annual energy use (kBtu/sf/yr) and percent savings compared to air-source heat pump

Air-Source City Heat Pump Ground-Source HP2 VRF (air-source) Ground-Source VRF HP (HP)1 kBtu kBtu % Savings kBtu % Savings kBtu % Savings Billings 65.3 46.0 30% 46.2 29% 42.5 35% Phoenix 65.9 51.8 21% 45.5 31% 40.9 38% Denver 59.5 44.3 26% 41.5 30% 40.4 32% Salt Lake 60.7 45.4 25% 40.3 34% 38.8 36% Fargo 72.8 48.2 34% 63.2 13% 44.7 39% Lincoln 72.9 49.3 32% 47.2 35% 42.7 41% Dallas 65.2 52.8 19% 43.8 33% 42.6 35% Kansas City 73.5 49.3 33% 46.2 37% 43.5 41% Seattle 54.9 43.9 20% 34.7 37% 34.6 37% Portland 56.5 44.6 21% 36.0 36% 35.3 38% Median Energy Use 65.3 47.1 28% 44.6 32% 41.7 36% & Savings

1 EER = 10.0, Seasonal Energy Efficiency Ratio (SEER) = 13.0, Heating Season Performance Factor (HSPF) = 5.0. Air-source heat pumps are commonly used in assisted living facilities, hotels, etc. 2 EER = 15.7, Coefficient of Performance (COP) = 3.3

net-zero energy. Little Deschutes Little Deschutes Lodge Lodge is a 26-unit complex with on-site laundry, a community room, a reading room, and two computer centers. Even with these amenities and features, the total gas and electric bills for the facility, divided by the number of apartments and by 12 months per year, came to only about $37 per month Engineering, Inc. in Portland, • Trenches spaced 12 feet on per apartment! Little Deschutes Oregon (http://www.solarc-ae. center. Lodge’s site EUI is only 29 kBtu/ net/), includes the following • Overall area of the piping square foot/year, compared to components: field is approximately about 70 kBtu/square foot/year for • 28 horizontal trenches, 50,000 square feet. an average dorm unit as calculated each approximately 150 • Four heat pumps (Mit- using Energy Star’s Portfolio Man- feet long. subishi City-Multi PQRY ager. This project has a Portfolio • Header piping at 6 foot P96TGMU, 8 tons each) Manager score of 95, modeled as a depth, trench piping at 9 serve the apartments, dorm, which means that it is more foot maximum depth. office, reading and fitness efficient than 95 percent of other • 600 feet of 1-inch pipe per rooms. similar units. trench, with four pipes • One Florida Heat Pump spaced evenly in a 3-foot- (ES-070, 5.5 tons) serves The Little Deschutes Lodge design wide trench. the community room and from SOLARC Architecture and kitchen. Energy Efficiency Factsheet: Ground-Source Variable Refrigerant Flow Heat Pumps • Page 6

• One 300 cfm energy The U.S. Department of Hous- • The value of ground-source recovery ventilator serves ing and Urban Development systems is more evident in the community room and (http://portal.hud.gov/hudportal/ extreme climates. kitchen, and one 800 cfm HUD?src=/about/mission) was • Ground-source systems are unit serves the rest of the created to help advance affordable invariably more expensive building. housing. And, as stated in this than air-source systems, • Ducted units in apartments, article, Moving Toward Zero Energy so in each case the ductless in common spaces. Homes (http://www.nrel.gov/docs/ engineer will need to do a • A desuperheater is used for fy04osti/35317.pdf), produced for cost-effectiveness analysis preheating hot water. the U.S. Department of Energy by to determine if the extra • The solar thermal system the National Renewable Energy cost of the ground-source is thermally connected to Laboratory, the goal for residential system can be justified. the ground loop to take housing should be net-zero energy. • Air-source VRF projects advantage of solar energy bid by experienced VRF when advantageous. At www.energystar.gov, some stud- installers are coming in at ies show that utility costs represent about $14-18/square foot. Maximizing Efficiency the single largest controllable cost Ground-source systems in an apartment community – can cost approximately and Minimizing typically accounting for 25 to 35 $30/square foot. Systems Maintenance percent. Reducing energy use by combining ground-source For affordable housing to be 15 percent in a typical 250-unit with VRF will be slightly viable, operating and maintenance master-metered community will more. For sites requiring a costs need to be as low as possible increase net operating income, lot of earth work anyway, so property owners can hedge and can enhance asset value like a school with playing against rising utility costs and by over $1 million (using a 6 fields, large parking lots, rising operating and maintenance percent capitalization rate). In a etc., the added cost of costs. In addition, since the similarly sized individually metered trenching for the ground- majority of affordable housing is community, this same savings source piping may be less, sponsored and/or developed by may increase asset value by over making a ground-source non-profits, the owners need to be $200,000 annually. system more attractive. able to cover all of their operating • The cost premium for a expenses, including debt cover- Conclusions ground-source VRF heat age, so they do not lose money. Based on modeling of the multi- pump system will have to Having a very energy efficient unit assisted living building using be weighed against the HVAC system can go a long way Energy Pro software, we can draw advantages, but if you to help achieve these goals. This is the following conclusions: are striving for maximum especially important in light of the • Ground-source VRF heat efficiency, consider install- fact that property owners can only pump systems can reduce ing a ground-source VRF raise rents to the extent that the energy consumption for heat pump system. area median income (AMI) of the heating and cooling by county increases on a percentage as much as 32-40 percent basis. over the current energy To print additional copies of code minimum efficiency this factsheet, please down- in many locations and load it from applications. http://www.energy.wsu.edu/ Documents/EEFactsheet-GSHP- Feb2011.pdf Energy Efficiency Factsheet: Ground-Source Variable Refrigerant Flow Heat Pumps • Page 7

About the Author Marcia L. Karr, P.E. Marcia Karr, P.E., an Energy Engineer at the Washington State University Extension Energy Program, is a licensed mechanical engineer with over 30 years of experience in commercial building design, construction and maintenance. She performs energy audits for commercial buildings, and provides technical assistance to commercial building owners, operators and builders in exploring energy saving opportunities. Karr’s previous positions include code plan reviewer, union trades manager, design/build engineer, field construction engineer/project coordinator, and HVAC/plumbing designer (commercial, institutional and residential).

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WSUEEP11-010 • March 2011 Energy Efficiency Factsheet: Ground-Source Variable Refrigerant Flow Heat Pumps • Page 8