With energy prices continuing to rise, the costs of heating and cooling commercial buildings are straining the operating budgets of many commercial enterprises. To best serve their customers, HVAC contractors can take advantage of an HVAC load calculation program, such as Chvac, by Elite Software, to assure optimal sizing of heating and cooling equipment for a new building or retrofit.
Proper sizing of the equipment avoids oversizing, a common outcome of ballparking the sizing. Oversizing not only carries a more expensive initial cost than necessary, it also results in short cycling. This hurts energy consumption and affects comfort during cooling because the system should run almost continuously during peak loads in order to ensure the air is properly dehumidified.
Chvac (www.elitesoft.com, 800-648-9523) is an HVAC load calculation program for commercial buildings. It is designed to size heating and cooling equipment correctly, taking into consideration a full complement of specific project details. The program quickly and accurately calculates peak heating and cooling loads using either the ASHRAE cooling load temperature difference (CLTD) method or the newer ASHRAE Radiant Time Series method (RTS). You can switch back and forth between RTS and CLTD for any project.
In order to properly size the equipment, the software compiles five types of data: general project, outdoor design data, building material, air handler and specific zone.
The general project data includes the project and client name, designer, building opening and closing hours, internal operating load schedules and desired safety factors. Outdoor-design data includes summer and winter outdoor-design conditions and the desired ventilation and infiltration rates.
The building material data includes the definition of master building material types for roofs, walls, partitions, glass sections and exterior shading. The program includes a user-defined material library for saving data on common types of material.
For air-handler data, information is gathered on fan and terminal type, the desired heating and cooling supply air temperatures, and duct heat gains and losses.
Zone data includes the zone name, floor length and width, number of people, equipment and lighting watts, external shading data and specific roof, wall, partition, floor and glass data.
Chvac allows an unlimited number of zones which can be grouped into up to 100 air handling systems. It is also possible to group zones under VAV boxes, allowing the solution to compute, at once, diversified peak loads at four levels: zone, VAV box, air system and total building. The solution allows 30 walls, 30 windows and 12 roofs per zone.
The program automatically looks up all cooling load and correction factors necessary for computing loads. It holds outdoor-design weather data for more than 2,000 cities from around the world and others can be added.
Chvac includes a specific drop-down help window for just about every input. It also performs extensive checks on data entered, alerting users to any problems, such as a wall with too much window area or a coil temperature for an air handler outside of the expected range.
Detailed reports list the general project data, detailed zone loads, air handler summary loads, outside air loads, total building loads, building envelope analysis, tonnage requirements, CFM air quantities, chilled water flow rates (if applicable) and complete psychrometric data with entering and leaving coil conditions.
Other capabilities include ASHRAE Standard 62 analysis, automatic building rotation, 360 degree wall orientations, tilted glass, exterior shading, internal operating load profiles, variable indoor design temperatures, people diversity, pretreated outside air, seasonal infiltration and ventilation rates, reheat loads, duct gains and losses, and return air plenums.
After sizing the equipment correctly, Chvac users can take advantage of a free downloadable building energy use analysis tool, eQuest (www.energydesignresources.com/Resources/SoftwareTools/eQUEST.aspx) to determine how to provide the equipment at the lowest cost. Provided by the government, eQuest provides energy analysis using data imported from Chvac. Using the data from the file, eQuest will calculate operating costs of equipment and, if desired, verify LEED certification.
The program uses a building creation wizard that walks users through all the data-entry steps to gather all information about the building design that would impact energy use and that provides choices of component and system options as well as suggested “intelligent defaults” for each, based on the data gathered earlier, in the description process. The solution automatically skips steps that do not apply to your design and offers you the opportunity to “bail out” of the description process once you reach the desired level of detail. At that point, the wizard fills in any missing data using the program's “intelligent default” process.
After compiling a building description, eQUEST produces a detailed simulation of the building and an estimate of how much energy it would use based on factors such as walls, windows, glass, people, plug loads and ventilation. Graphically displayed simulation shows estimated overall building energy on an annual or monthly basis, as well as comparative performance of alternative building designs.
Bill and Patti Feldman are freelance writers for magazines, building product manufacturers and other companies on a broad range of topics. They can be reached at email@example.com.