Variable Refrigerant Flow (VRF) Heat Pumps
Heat Pumps: Variable Refrigerant Flow (VRF) vs. Conventional
An advanced variable-speed heat pump system can save energy when compared with conventional air-to-air heat pumps due to better part-load efficiencies, heat recovery, and reducing or eliminating duct losses.
Item ID: 200
Technical Advisory Group: 2009 HVAC TAG (#2)
Technical Advisory Group: 2015-1 Commercial HVAC TAG (#11)
Average TAG Rating: 3.7 out of 5
TAG Ranking Date: 03/10/2015
TAG Rating Commentary:
- Needs research and development of Design Guidelines to define how they should be most efficiently applied. I have used them in the most efficient buildings that we have designed, but I have also seen VRF in inefficient buildings.
- Applications for this technology vary so much that it will likely remain custom; VRF savings have also varied, sometimes even negative savings, indicating a need for best practice guides.
- Every incentivized installation should be monitored. For example, the ASHRAE HQ in Atlanta got a top-to-bottom retrofit, with one floor getting a ground-source heat pump (GSHP) and the other multi-split. GSHP is performing much better. Why? Multi-splits have huge potential (avoiding the pressure issues that come with many forced air systems), but much more US experience is needed.
- Still waiting on proven savings results
- These are commonly used in other countries - they can exchange the heating and cooling from different zones in a building and save on air distribution. A grreat technology that will be needed for zero-net-energy (ZNE) buildings.
- We definitely need additional field studies to determine appropriate applications so this technology can see some repeatable efficiency success.
- Promising solution for the right applications and when installed and operated properly
Variable Refrigerant Flow (VRF) systems are typically all-electric systems that use heat pumps to provide space heating and cooling to building spaces (ECW, 2014). They are capable of serving multiple zones in a building, each with different heating and cooling requirements. These systems have the ability to modulate the amount of refrigerant sent to each zone in accordance with conditioning requirements (ECW, 2014). In contrast, conventional HVAC systems deliver air or water and operate on a full-on or full-off schedule [Johnson Controls]. In contrast, VRF systems efficiently deliver refrigerant at variable rates and exact amounts to spaces that require it. VRF heat recovery units allow multiple indoor units to operate in simultaneous heating or cooling modes while connected to a single outdoor unit. While VRF used to be more distinct from ductless heat pumps (DHP), which originally included only one indoor and one outdoor unit, DHP units can be integrated into a larger VRF system.
VRF technology was perfected in Japan and introduced to the U.S. market in the early 2000s. The refrigerant flows through pipes between an outdoor unit and indoor fan coil units that condition and recirculate indoor air. VRF systems have the following efficiency features: variable speed fans to provide modulation of the indoor and outdoor units, smaller zones, linear expansion valves, a variable speed compressor, heat recovery among zones, and minimal losses from ducts (Karr, 2011). Savings are better when this technology is coupled with ceiling fans to enhance air distribution as well as a dedicated outdoor air system (DOAS) that includes heat recovery. Systems come in small sizes for residential and small commercial buildings, and in large configurations up to several hundred tons for high-rise buildings. The smaller versions, known as ductless heat pumps, are addressed in more detail in other records in this database. Energy codes typically mandate SEER ratings for heat pump and chiller systems of around 12. VRF units can have an IEER (integrated EER) value in the mid-20s with a heating COP exceeding 3.4 at 47⁰F.
Compared with air-to-air heat pumps, VRF offers energy savings due to better part-load efficiencies, heat recovery, smaller zones, and reduced duct losses. Annual energy savings depend on climate zone. Using Energy Pro building modeling software, annual heating and cooling energy savings for a 25,000 square foot assisted-living building are estimated at 37% in Seattle, WA; 36% in Portland, OR; and 29% in Billings, MT (Karr 2011). A BPA study uses a more conservative annual energy savings estimate of 20% (EES Consulting, 2012).
The installed cost of VRF systems is about $18 per square foot served, while a code-minimum system could cost about $12 to $15 per square foot. VRF systems can be very cost-effective in new construction applications or when an existing system has reached the end of its useful life and must be replaced. While VRF can be employed as a retrofit technology, cost-effectiveness is reduced because the full cost of purchasing and installing the equipment must be recovered instead of only the incremental cost. VRF systems also offer sophisticated controls for demand response, operations, and maintenance alerts.
Baseline Description: Code-minimum heat pump in an office building
Baseline Energy Use: 10.5 kWh per year per square foot
The 2009 Commercial Building Stock Assessment (CBSA) gives the actual electrical building EUI's for various types of heating and cooling systems (Table D-EA5). Office buildings with electric heating and cooling have an EUI of 20.1 kWh/sf/year. Office buildings with no electric heating or cooling use only 8.2 kWh/sf/year (for non-HVAC end uses), indicating that the HVAC heating and cooling energy use is 11.9 kWh/sf/year. (For all commercial buildings, the corresponding numbers are 19.9 and 9.4 kWh/sf/year, respectively.) Because this technology can be applied to many types of non-office commercial buildings, a baseline energy use of 10.5 kWh/sf/year is assumed (NEEA, 2009).
Manufacturer's Energy Savings Claims:
Currently no data available.
Best Estimate of Energy Savings:
"Typical" Savings: 20%
Low and High Energy Savings: 5% to 50%
Energy Savings Reliability: 5 - Comprehensive Analysis
Savings estimates for VRF systems range from 5% to over 50% compared with traditional HVAC equipment, but there are cases of increased energy use in poor applications. This wide range is due to variation in design, climate, and baseline. For Northwest climates, the study for BPA assumes 20% HVAC savings for all VRF systems (EES Consulting, 2012).
From 2010 to 2014, BPA funded a study comparing the performance of HVAC systems in two nearly identical low-income housing units. One used a central ground source heat pump (GSHP) while the other used VRF, and both provided space conditioning and domestic hot water. Overall, both methods achieved energy savings of about 20% to 30% compared to typical new multifamily construction, yet these savings were less than anticipated. Overall savings from water heating energy use, specifically, was approximately 30% compared to a typical non-heat pump water heating system in a multifamily building, while savings almost double this level were expected. In part this is due to the VRF system’s inability to provide water over 108 degrees F, causing additional heat to be provided with electric resistance heating.
Surprisingly, the VRF system performed relatively poorly for space heating energy. This was apparently due to electric resistance space heaters operating in the mechanical room and crawlspace (due to fire code, not energy code) with poor thermostatic control as well as poorly maintained condensing unit coil. These are the sort of details that greatly impact overall energy use. A number of useful lessons were generated by this study (Heller, Oram, and Cejudo, 2014).
Energy Use of Emerging Technology:
8.4 kWh per square foot per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
This technology combines both the VRF systems with internal/external heat recovery and those without heat recovery. As it could technically be used for conditioned space in virtually any commercial building, the entire commercial building stock in the Northwest is used for technical potential (including a small overlap with commercial sector ductless heat pump applications). The numbers are taken from preliminary updated numbers from the 2013 update to the Commercial Building Stock Assessment (CBSA), specifically the estimates from early January 2014, before the update was completed. These estimates were multiplied by the percentage of commercial space that is conditioned based on the 2009 CBSA. It is not appropriate for buildings with high ceilings, such as big box stores. This is taken to be 50% of retail and grocery space. We can only count electrically heated buildings for the purposes of BPA savings potential because they are significantly more cost-effective than buildings with non-electric heat. According to the CBSA, about 30% of commercial buildings are heated with electricity. Buildings with non-electric heating may also benefit from VRF but will not be as cost-effective.
Comment: As a point of reference, a study by BPA concluded that the 20-year technical potential for VRF was 4.64 aMW (EES Consulting, 2012).
Commercial Floor Space Appropriate for VRF with Internal and External Heat Recovery
Regional Technical Potential:
| || Total Floor space || -s.f. Warehouse || non-Warehouse || % Conditioned || Applicable Space || 50% Retail & Groc. || Appropriate Space ||Elect. Ht. |
| Source || (NEEA, 2014) || (NEEA, 2009 App C) || || || || (NEEA, 2009 App C) || || |
| || 3,118,000,000 || 173,000,000 || 2,945,000,000 || 87.0% || 2,562,150,000 || 240,000,000 || 2,322,150,000 || |
1.47 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: square foot
Emerging Technology Unit Cost (Equipment Only): $18.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.00
Baseline Technology Unit Cost (Equipment Only): $15.00
There is some incremental cost for this technology, but this has not reduced its steadily increasing market penetration. Manufacturers have succeeded in selling this technology by emphasizing its energy efficiency and other benefits. The installed cost of VRF systems is about $18 per square foot of conditioned space, while a conventional air-source heat pump system costs about $12 to $15 per square foot. These cost estimates are consistent with the 5% to 20% incremental costs (13% mid-point assumed as the typical value) from the BPA study (EES Consulting, 2012).
Simple payback, new construction (years): 15.9
Simple payback, retrofit (years): 95.2
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
VRF systems havecost-effectiveness advantages when (Thornton, 2012):
- The existing HVAC system is inefficient and/or near the end of its useful operating life;
- Energy costs are high;
- The system is being considered for an older or historical building;
- The existing system has a lack of cooling or inadequate cooling capability;
- The system is a part of new construction that is able to reduce floor-to-floor heights, or increase useable floor space;
- The new system is replacing VAV systems with electric reheat;
- Fan systems are inefficient;
- Ductwork is leaky or poorly designed.
Reference and Citations:
Measure Summary Report: Variable Refrigerant Flow
Bonneville Power Administration
Total Pacific Northwest Building Stock Based on Preliminary Numbers from the 2013 Update to the CBSA
Northwest Energy Efficiency Alliance
Northwest Commercial Building Stock Assessment (CBSA): Final Report
Prepared by the CADMUS Group for the Northwest Energy Efficiency Alliance
Danfoss Introduces World’s First Commercial Variable Speed Scroll Compressor for Air Conditioning with R-410A at AHR in North America
Danfoss Ireland, Ltd.
Ground-Source Variable Refrigerant Flow Heat Pumps: A solution for Affordable Housing, Assisted Living, Hotels and Dorms
Washington State University Extension Energy Program
Variable Refrigerant Flow Systems
Prepared for the General Services Administration by Pacific Northwest National Laboratory
Heller, Oram, and Cejudo,
Multifamily Case Study: Geo-Exchange vs. VRF Space and Water Heating: Final Report
Variable Refrigerant Flow (VRF)
Energy Center of Wisconsin