The aims of a heating, ventilation, and air conditioning (HVAC) systems include everything from maintaining comfortable temperature and humidity levels, to supplying adequate fresh air and removing possible pollutants from the air, all while creating minimal inconvenience for occupants. With this wide range of tasks, it’s easy to understand how as much as 40% of a building’s energy use can go toward operating an HVAC system (USDOE). Therefore, working to establish and maintain an efficient HVAC system within your building can significantly reduce energy needs. Upgrading to efficient equipment, properly maintaining established equipment, and installing control devices can all contribute to HVAC energy savings.
A central plant system, which utilizes a commercial boiler, is the most common form of heating system for large buildings such as commercial buildings or multi-family residences. The size and capacity of the system is dependent on the building’s peak energy load. An efficient boiler system would meet a building’s heating demands during peak load while still operating efficiently during partial loads. The most common way to rate the efficiency of a boiler system is by looking at its thermal efficiency, or the effectiveness of the heat transfer from the combustion process to the water or steam in the boiler.
The simple equation to derive the thermal efficiency of the boiler of heater is:
Thermal efficiency percent = (Output Energy)/(Input Energy X 100)
Buying Efficient Equipment:
The Federal Energy Management Program (FEMP) provides efficiency guidance for purchasing an efficient commercial boiler. The values listed in the table below are the minimum efficiency values required for a system to be considered efficient.
FEMP also offers an energy cost savings calculator to allow users to determine cost-effectiveness of a new system, which can be found here: Energy Cost Savings Calculator for Commercial Boilers.
|TABLE 1. EFFICIENCY REQUIREMENTS FOR COMMERCIAL BOILERS|
|Product Class||Rated Capacity||Fuel||Heating Medium||Thermal Efficiency* (%)|
|Small Gas-Fired Hot Water||≥300 kBtu/h and ≤2,500 kBtu/h||Gas||Hot Water||Et ≥ 95.0|
|Large Gas-Fired Hot Water||>2,500 kBtu/h and ≤10,000 kBtu/h||Gas||Hot Water||Et ≥ 94.0|
|Small Gas-Fired Steam||≥300 kBtu/h and ≤2,500 kBtu/h||Gas||Steam||Et ≥ 81.0|
|Large Gas-Fired Steam||>2,500 kBtu/h and ≤10,000 kBtu/h||Gas||Steam||Et ≥ 83.0|
|Small Oil-Fired Hot Water||≥300 kBtu/h and ≤2,500 kBtu/h||Oil||Hot Water||Et ≥ 85.5|
|Large Oil-Fired Hot Water||>2,500 kBtu/h and ≤10,000 kBtu/h||Oil||Hot Water||Et ≥ 86.0|
|Small Oil-Fired Steam||≥300 kBtu/h and ≤2,500 kBtu/h||Oil||Steam||Et ≥ 84.0|
|Large Oil-Fired Steam||>2,500 kBtu/h and ≤10,000 kBtu/h||Oil||Steam||Et ≥ 85.5|
|*Based on Hydronics Institute, Method to Determine Efficiency of Commercial Space Heating Boilers (HI BTS-2000, Rev. 06.07).|
Energy Star guidelines are also available for evaluating the relative efficiency of HVAC equipment like boilers, fans, and air conditioners as well as many other appliances. High efficiency equipment is given Energy Star certification. Certified products and their manufacturers are listed on the Energy Star website: http://www.energystar.gov
Incentives and rebates from local utilities are typically available for a variety of equipment upgrades to electric HVAC systems.
Getting The Most Out Of Your System:
- Programmable thermostats and time clocks can be installed as part of the building’s heating system. This enables the system to be self-regulating based on pre-determined time or temperature settings set by the user.
- Insulating and sealing equipment, such as bare pipes, helps reduce heat loss from the system to the outside world. This can increase system efficiency by up to 20%
- Check your water temperature set points on your boiler or water heater. If they are too high, adjust accordingly.
- Heating efficiency can be greatly inhibited by scale build-up within the boiler.
Water treatment can be added to help prevent this.
- Ensure water levels in the boiler are maintained to prevent damage to the system
- Include equipment tune ups as part of your regular maintenance routine. Ensuring the existing system is running as planned.
For a central plant system typical in commercial buildings, chillers and cooling towers provide a building’s cooling needs. A central plant system uses a variety of pumps, pipes, control valves, and ductwork to distribute heat or cooling throughout the building. A chiller uses electricity to remove heat from the chilled water loop, and subsequently the building. This removed heat is then released to the outside world via a cooling tower. A water cooled chiller is typically more efficient than an air cooled chiller due to added cooling effects from evaporation. However an air-cooled chiller does not require a cooling tower.
The diagram at the right illustrates the basic mechanics of a chiller unit. The chiller removes heat from a liquid by employing vapor-compression or absorption refrigeration.
In a vapor-compression cycle, a refrigerant in vapor form is pressurized by a compressor, which in turn heats the refrigerant. This vapor then flows through condenser coils. The hot refrigerant gives off heat to the outside air, which cools down the vapor into a liquid form. However, it is still at high pressure. The liquid refrigerant then travels through an expansion valve which converts some of the liquid back into a vapor by lowering the pressure. Finally, the vapor/liquid refrigerant passes through an evaporator. The refrigerant picks up heat from inside the space, which turns any remaining liquid into a vapor.
Buying Efficient Equipment
The Federal Energy Management Program (FEMP) provides buying guidance in this area as well. Below is a table of FEMP certified efficient chiller values. The table is categorized by type of chiller and load size application, which depends on a building’s cooling needs.
While the code EER is at 10, but high efficiency CUs have an EER of 12 or higher and rebates are only offered for EERs of 12 or higher.
|TABLE 1. EFFICIENCY REQUIREMENTS FOR WATER-COOLED ELECTRIC CHILLERS (KW/TON)|
|Chiller Type||Capacity (tons)||Full-Load Optimized Applications
(products must meet both levels)
|Part-Load Optimized Applications
(products must meet both levels)
|Full Load Efficiency||Integrated Part-Load Value||Full Load Efficiency||Integrated Part-Load Value|
|Positive Displacement||< 75||0.736||0.600||0.780||0.500|
|75 to 149||0.720||0.560||0.750||0.490|
|150 to 299||0.651||0.540||0.680||0.440|
|300 to 599||0.610||0.520||0.625||0.410|
|150 to 299||0.610||0.550||0.635||0.400|
|300 to 399||0.560||0.520||0.595||0.390|
|400 to 599||0.560||0.500||0.585||0.380|
Energy Star guidelines are available for evaluating the relative efficiency of HVAC equipment like boilers, fans, and air conditioners as well as many other appliances. High efficiency equipment is given Energy Star certification. Certified products and their manufacturers are listed on the Energy Star website:
Incentives and rebates from local utilities are often available for efficient upgrades to electric systems.
Getting The Most Out Of Your System
- Insulate your cooling system equipment and pipes to prevent energy losses to the outside world.
- Utilize cool nighttime air when available to lessen the work load of your system.
- Install programmable thermostats
- Include regular tune-ups as part of your equipment maintenance routine.
A typical air handling unit provides air movement, air filtration, heating and cooling of air, and humidity control. In a central plant design, secondary air handling units are used to distribute comfortable, clean air to different zones. Commonly, a Variable Air Volume (VAV) system is used which allows one system to control several zones. Each zone has its own terminal unit that regulates cooling and heating loads and maintains the minimum ventilation standards for that zone. Various controls can be installed within a ventilation system to help save energy.
Heat and moisture exchangers allow cool incoming air to be warmed by hot outgoing air and vis versa. This helps to reduce overall system work load thus saving energy
Getting the Most Out Of Your System:
- Replacing filters at least every three months can improve both indoor air quality as well the efficiency of your HVAC system.
- Insulate and seal ducts and pipes along distribution routes. This ensures air stays at the appropriate temperature as it travels to its destination and can increase system efficiency by up to 20%.
- Ensure the ventilation system is properly sized for your building.
- Work with a professional to optimize VAV controls.