VRF System (Courtesy of Jacco & Associates)

Variable Refrigerant Flow Technology Provides Opportunity & Energy Savings

By Greg Drensky

The HVAC industry is one of constant change and improvement. One of the most recent technological advances is the introduction into the U.S. of variable refrigerant flow (VRF) technology. VRF was first developed in Japan over 20 years ago, where there is a tremendous demand for energy efficient HVAC products and space-saving designs due to high utility costs, the large number of retrofit projects, and escalating construction costs. In Japan, VRF systems are used in approximately 50% of medium-sized commercial buildings (up to 70,000 square feet) and 33% of large commercial buildings (over 70,000 square feet). It is now sweeping across the U.S. for many of the same reasons. The world headquarters for the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) in Atlanta is currently being built with half of the floor space utilizing VRF technology to showcase the energy savings, environmental friendliness and indoor comfort. They are planning to obtain LEED (Leadership in Energy and Environmental Design) Gold certification for the building.

At the heart of the VRF system is an air-cooled heat pump. These heat pumps are different from what we commonly see due to a variable speed compressor. The variable speed compressor allows the heat pump to distribute the exact amount of refrigerant required to satisfy the building load. In principle it operates similar to that of a throttle on an automobile. When you need to increase the speed of your car, you depress your throttle and accelerate the car. When you need to slow down you slowly release the throttle. Typical heat pump systems have two speeds, on (full throttle) or off. Imagine how bad your gas mileage would be if all you could do is floor the throttle every time you needed to accelerate? Imagine trying to maintain a constant speed? With VRF you end up with energy savings, indoor comfort and long life by modulating the compressor as opposed to staging it off and on.

Also as opposed to common heat pumps, VRF heat pumps are able to heat your space well into negative outdoor temperatures, which oftentimes eliminates the need for supplemental electric heaters. VRF heat pumps can be placed either outdoors or indoors. By placing the heat pump outdoors you eliminate the need for any mechanical rooms. You also have the ability of running up to 985 feet of piping, including up to 165 feet of vertical distance, making it ideal to place a unit on the roof of a multi-story building and feeding the floors below. This gives the owner, architect and engineer flexibility in their building designs as well as construction savings by eliminating mechanical rooms. If your worried about sound you'll also be comforted to know that systems such as Sanyo's ECOi heat pumps have NC values as low as 52dBA, which is quieter than a typical conversation (60dBA).

The indoor evaporators are quite flexible in design and capacity, and up to 40 indoor units can be connected to a single heat pump with common piping. They can be wall-mounted, concealed in a ceiling plenum, placed into a drop ceiling (semi-concealed), or ceiling suspended. This flexibility bodes well for retrofit designs as well as new construction with styles available for every room and application. The evaporators are fitted with electronic expansion valves and multiple speed blowers. As the room load increases or decreases, the electronic expansion valve reacts accordingly to provide the proper amount of heating or cooling directly into the space. Depending on the difference between the room temperature and setpoint, the evaporator fan adjusts its speed for either heating, cooling or temperature maintenance. Think back to the throttle technique. Each one of these devices gains energy savings by providing specific control of your system and not over- and under-shooting.

To read the rest of this article, download the May issue of Properties Magazine now. [May 2008; download PDF; 7.6 mb]