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Heating, Ventilation & AC Basics

The purpose of heating, ventilation and air-conditioning systems (HVAC) is to heat, cool, control humidity and ventilate (introduce fresh air into) the building. Employee and customer comfort is the first priority of HVAC systems. HVAC systems are among the largest energy end-uses in commercial buildings throughout this region.

There are many types of heating, cooling, and ventilation systems. Heating systems include boilers, furnaces, electric resistance elements and heat pumps. Cooling systems include window air conditioners, packaged (Direct Expansion or DX) units, heat pumps, chilled water systems and evaporative coolers. Ventilation and air distribution may be directly from the HVAC fan into the space, or through a network of ducts and/or air plenums. HVAC systems can be quite complex both in equipment and controls, and changes in one part of the system will have impact on other elements.

HVAC and Energy Use
HVAC systems can waste energy in four basic ways:

· Thermal Losses . Heated or cooled air will lose some of its thermal property through convection or conduction as it travels through the ducts of the air distribution plenums.

· Improper Sizing . HVAC systems are often oversized to ensure that sufficient air conditioning is always available, but this can also lead to significant operating inefficiencies.

· Excessive Demand . Increased HVAC load due to an inefficient building envelope or waste heat generated by lighting and equipment can cause the HVAC system to operate at higher levels for longer periods of time than is necessary.

· Poor Control Strategies . Temperature settings, hours of operation, seasonal conversions and other methods of control are frequently not given adequate consideration or implementation.

· Inefficient Equipment . Often older HVAC equipment and inexpensive equipment is not as efficient as other available HVAC technologies.

Reducing HVAC Energy Use
There are four simple guidelines to reducing HVAC energy use:

1. Reduce operating hours by turning systems off when they're not needed.

2. Improve operating efficiency of the systems by adjusting temperature settings and performing regular cleaning and maintenance.

3. Replace existing components or systems with more efficient equipment.

4. Increase system efficiency by installing improved controls and advanced control strategies.

No-Cost Opportunities

Manual Control
HVAC operating hours can be reduced in many commercial buildings by simply turning off HVAC systems when they are not needed, for example, when the building or zone will be unoccupied for an extended period. Operable windows and fans provide air movement and natural "free" cooling on moderate days, which are prevalent through much of the year in this area. Ventilating with mild outside air is much less expensive than mechanically cooling the building air, which is warmed by people, lights and equipment.

Adjust Temperature Settings
Lowering thermostat settings just a few degrees during the heating season and raising thermostat settings during the cooling season is an easy and effective method of saving HVAC energy. In this region, reducing the heating temperature by an average of just 3 degrees throughout the heating season will reduce heating energy usage by about 13%. Energy savings are even greater, per degree, for raising air conditioner thermostat settings than for reducing heating levels.

Some experimentation will be necessary to find the optimal settings that maintain comfortable conditions for employees and customers. Allowing and encouraging employees to dress comfortably and seasonably will make it easier to adjust thermostat settings without creating discomfort.

Low-Cost Opportunities

Building Envelope and Lighting Improvements
Improvements in the thermal properties of the building envelope and in the efficiency of the lighting systems will reduce the load on the HVAC system. Any improvement to the building that reduces summer heat gain and/or winter heat loss will result in HVAC energy cost savings.

Furnace and Boiler Maintenance
Periodically perform combustion efficiency testing and combustion rate adjustment for gas-fired heating equipment. Replacing air filters and cleaning intake screens will also help gas-fired equipment operate more efficiently. Good maintenance practices can reduce fuel costs by 5-10%.

Cooling System Maintenance and Cleaning
Air conditioners, heat pumps, chillers and cooling towers all work by thermal transfer, moving heat from one place to another. Heat transfer surfaces, such as cooling coils, condenser coils, heat exchangers and evaporator surfaces, should be clear of dirt, grease and other obstructions. Select a technician to regularly inspect, treat and maintain the major cooling equipment in your building.

Ductwork Maintenance
Air duct joints and elbows should be appropriately sealed. Damaged or disconnected duct sections should be repaired and air filters should be regularly replaced. Ductwork in unconditioned spaces, such as on roofs and in attics, should be insulated. Energy is often wasted in commercial buildings due to leaks and poor insulation in HVAC ductwork.

System Balancing
Select an HVAC technician to periodically balance the HVAC air and water distribution systems. This maintenance procedure will help maintain appropriate and efficient space temperature control throughout the building.

Install Programmable Thermostats
Programmable thermostats are simple microprocessor-based units that accurately maintain system start-up and set-back schedules, and eliminate unnecessary HVAC use during hours when the building is normally not occupied. Improved controls are a small investment that may yield large improvements in HVAC energy efficiency.

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