Even with today’s falling energy prices, facility managers are looking for ways to reduce the energy use of HVAC systems. New technologies and improvements in existing technologies are giving facility managers options. While advances can be seen in practically all HVAC systems, some of the most significant advances are coming in three particular areas: variable refrigerant flow systems, rooftop units, and geothermal systems.
VARIABLE REFRIGERANT UNITS
Variable refrigerant flow (VRF) systems have been used in Asia and Europe for nearly three decades, but have only recently made inroads in the U.S. In conventional systems, one condensing unit is connected to one evaporator, providing conditioned air to one area of a building. If the system is to supply air to more than one area, ductwork must be added, along with zone controls. While this configuration works, it is not the most flexible or energy efficient, and often results in complaints from building occupants.
VRF systems offer an alternative. In these systems, a single outdoor condensing unit is piped to multiple indoor fan coil units. Refrigerant is circulated in the system through either a two- or three-pipe system. In two-pipe systems, all fan coil units or zones must be in either heating or cooling mode. Three-pipe systems have the ability to simultaneously heat some zones while cooling others.
ROOFTOP HVAC SYSTEMS
Rooftop HVAC systems are one of the most common ways of providing heating and air conditioning to commercial and institutional buildings. Developed as a simple bare-bones solution to the HVAC needs of low-rise buildings, they are available in a wide range of capacities and configurations. Their low first cost, and the fact they don’t take up valuable floor space in a building, have contributed to their popularity. But not everyone has been overjoyed about their widespread use. Maintenance managers have found them to be maintenance nightmares: difficult to service, prone to breakdowns, and inadequately protected from the elements.
With low cost being the primary driving force motivating both manufacturers and users, there has been little movement to improve the operating efficiency of their units beyond what energy codes require. Some manufacturers do offer a limited number of high efficiency options, but their use has been restricted by the competitive nature of the market and the fact that these features typically increase the cost of the rooftop unit.
Conventional heat pumps transfer heat to or from a building to the surrounding air. A geothermal system, also known as a water source heat pump, uses the earth as a source for heat during the heating season and a heat sink during the cooling season. While air temperatures can vary widely during both seasons, ground temperatures remain fairly constant, between 50 and 60 degrees F for most of the United States. These moderate temperatures result in a major boost in operating efficiency of the heat pump systems with their Coefficient of Performance (CoP) between 3 and 6 on a cold winter night. A conventional heat pump would have a CoP between 1.75 and 2.5 when operating under those same conditions.
Vertical geothermal systems use vertical boreholes similar to wells with a diameter of 4 inches sunk 100 to 400 feet below the surface. Inserted into each hole are two sections of pipe joined at the bottom by a U-bend. The hole is then backfilled with a thermally conductive slurry material to maximize heat transfer with the piping. Depending on the depth of the borehole, the soil conditions, and the temperature of the soil, each ton of heating or cooling capacity requires between one and two boreholes. All vertical sections are piped into a common manifold that is piped to the HVAC unit. Vertical geothermal systems are best suited for applications where land area is limited. Boreholes must be separated from each other by at least 15 feet to prevent interfering with the thermal conductivity of neighboring boreholes. Even then, the land area the systems require is much less than for horizontal systems. Their primary drawback is the cost to drill the required number of boreholes.
Pond Geothermal Systems
Pond geothermal systems are well suited for facilities with a sufficiently sized body of water on site. Piping is run from the facility’s unit to the pond, where coils of piping are installed in the water. The coils should be placed sufficiently below the surface of the water to prevent freezing, based on the local climate.
Of the three systems, the pond geothermal system is the least expensive to install due to the lack of boreholes and minimum trenching requirements. To be successful, though, the body of water must be big and deep enough to support the system year round.
All three types of geothermal systems have higher first costs than conventional heat pump systems. The reduced energy costs for the systems typically recover this difference in five to 10 years. Applying federal, state, and utility incentives when available will significantly shorten this payback period.
*Article source from www.facilitiesnet.com