Energy efficient HVAC systems – 101

Fouling

Definition: Dirt and dust buildup which occurs on the surface of A/C coils over time and can cause a loss of energy efficiency and excessive wear and tear on the compressor. Fouling may also lead to problems with indoor air quality and excessive mold buildup.

Figure 1-Clean coil vs. dirty coil

Effect on efficiency: ‘Operating an A/C unit with dirty coils (fouling) and/or filters and easily consume up to
37% more electricity as compared to an A/C unit with clean coils and filters. For example, consider a 10 ton air conditioning system operating for an average cooling season of 1,500 hours. When the coils are clean, it will cost approximately $1,650 to operate
for the season, given a typical Kw/hr cost and equipment SEER (efficiency). However, when the condenser
coil becomes dirty, the six-month cost of operation escalates to $2,268 . . . a 37% increase.’ Excerpt from Clean Coil Program. St. Louis: Nu-Calgon, 2007

Solution: Coils must be sprayed with an aluminum/nickel safe coil cleaner that is strong enough to break down the buildup. After the chemical reacts with the fouling, it must be thoroughly rinsed with copious amounts of water. Drain pans and drain lines should be cleared of all debris and coil (indoor unit), return plenum, and inside of air-handler should be sprayed with an aluminum/nickel safe sanitizer. Condensate water should be treated to prevent buildup of bacteria that causes foul odor. Fan blades should also be checked for any buildup, as this can cause a decrease in airflow and thus a decrease in efficiency.

HVAC Controls

Definition: Any electronic or mechanical device that controls an HVAC unit by monitoring temperature, air volume, or the level of a specific toxin, which may occur in an indoor environment.

Note: Typically, many commercial buildings have simple on/off type thermostats either being electronic or (rarely but) occasionally the simple mercury bulb type.

Effect on efficiency: ‘A typical A/C unit running constantly for one year will generally cost more to operate than the cost of the unit.’ SMACNA National Association. Energy Systems and Management Manual, VA, 1997

Solution: An energy-consuming device uses the least amount of energy when it is turned off. Quality, commercial grade, smart and programmable HVAC controls & thermostats should be installed by a professional to reduce the amount of time the HVAC unit runs during the season. Many businesses with simple on/off type thermostats who rely on their employees to turn the HVAC units off at night may be surprised to find out how often their HVAC unit runs all night while no one is in the building, wasting money and energy.

Duct Leakage

Definition: Areas in a sealed duct system where cold or hot air leaks into an unconditioned space, which causes the conditioned space to be heated or cooled in an inefficient manner.

Effect on efficiency: ‘Duct leakage contributes 10-30% of heating and cooling costs.’ Energy Efficient Building Construction in Florida. Florida: University of Florida, 2007

Solution: This is a very common problem in older commercial and residential buildings, where vermin may destroy ductwork, and is also occasionally found in newer buildings as well due to sloppy installation work. Problem areas may easily be detected by a duct leak inspection via infrared thermal imaging tools as well as duct pressure testing devices. If problem areas like the one illustrated in Figure 4 occur, the ductwork can usually be repaired inexpensively with tape, glue, and plastic straps. In some severe cases, some areas of ductwork may need to be replaced.

Refrigerant Undercharge/Overcharge

Definition: A lack or loss of refrigerant in a HVAC or refrigeration system which causes a unit to cool at a higher temperature, therefore causing the unit to run constantly, since it can not achieve the set-point temperature on the thermostat that has been set by the user. This problem will cause damage to mechanical components if left unresolved.

Effect on efficiency: “A refrigerant undercharge of 15% causes a 19.6% decrease in system (HVAC) efficiency.” Energy Efficient Building Construction in Florida. Florida: University of Florida, 2007

Solution: According to a recent study done by the EPA on central air conditioners and heat pumps, 41% of the systems
examined were undercharged and 33% were overcharged. Both scenarios cause an increase in energy use and premature failure. This is a very common problem with old or new leaking units and new split units installed by sloppy HVAC contractors and installers that do not have the proper charging tools and do not use proper charging techniques. New HVAC systems come with some refrigerant, but refrigerant must be added to compensate for the length of the variable copper pipes, which many installers neglect. In leaking units, the leak must be found and repaired. The best solution for determining the precise amount of refrigerant needed is by a qualified technician using a digital superheat and sub-cooling manifold gauge and a manufacturer’s charging chart.

The following are examples of energy saving technologies that can be used with most HVAC and Refrigeration systems to reduce energy consumption:

Variable Frequency Drives

Definition: A variable-frequency drive (VFD or VSD) is a device which controls the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor. Variable-frequency drives are widely used in ventilation systems for residential and commercial buildings. Variable-frequency motors on fans save energy by allowing the volume of air moved to match the system demand.

Effect on efficiency: “Variable frequency drives installed to reduce air-flow significantly can easily pay for themselves in under a year for a return on investment of over 100 percent.” Allient Energy. Variable Frequency Drives Page. 2008.

Smart Defrost Kits

Definition: A Smart Defrost Kit or SDK is typically used on a refrigeration system. SDK’s consists of an intuitive mini-processor that uses temperature and pressure sensors to monitor the refrigeration defrost process. The SDK takes time to learn the unique operations of a particular refrigeration system. After this short initial learning period, the SDK processes information such as suction pressure and temperature, cycle and defrost data, including duration and frequency of defrost cycles. Those information points are constantly analyzed and sorted by priority. Once the time clock within the system signals the next defrost, the SDK determines if the defrost is necessary. If it is not, then the SDK tells the time clock to skip this defrost. If enough ice has accumulated on the evaporator to warrant a defrost cycle, the SDK allows the system to defrost normally. By skipping unnecessary defrost cycles, the energy use of the refrigeration system is greatly reduced.

Effect on efficiency: Refrigeration systems with Smart Defrost Kits can expect to see $200 to $600 in estimated savings a year and power savings up to 9,500kWh a year.