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Chvac - Commercial HVAC Loads

Commercial Load Calculations Done Right

Chvac has been an industry leader in commercial load calculation software since 1979. Try Elite Software's flagship program today and see why so many professional engineers are choosing Chvac. Get both Chvac and EnergyPro (which Chvac links to) and you'll have the most powerful, user-friendly commercial load calculation/energy analysis combo on the market.



Chvac quickly and accurately calculates the maximum heating and cooling loads for commercial buildings. The cooling loads can be calculated with either the CLTD method or the new RTS (Radiant Time Series) method. The program allows an unlimited number of rooms which can be grouped into as many as 100 air handling systems. Chvac automatically looks up all cooling load and correction factors necessary for computing loads. In addition, it can look up outdoor design weather data for over 2000 cities located around the world. There is also provision for editing the weather data as well as adding data for other cities. Comprehensive reports list the general project data, detailed room 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 outstanding features 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.

Five Versions Available

There are five versions of the Chvac program; 2 room capacity ($299), 10 room capacity ($399), 50 room capacity ($599), 100 room capacity ($999), and unlimited capacity ($1499). Keep in mind that a room is a single space, and that rooms can be grouped into air handling systems which in turn make up the building. Rooms can optionally be grouped under vav boxes as well (zones). This allows Chvac to compute diversified peak loads at four levels in one run of the program: room, vav box (zone), air system, and total building. The maximum number of air handling systems allowed for any version is the number of rooms allowed or 100, whichever is the lesser. Each Chvac version is exactly the same with the exception of the room capacity and price. However, there is a generous upgrade policy. If at any time you decide to obtain a version of Chvac with greater capacity than the original one you obtained, all that is required is to pay the difference in price between the two versions.

Advanced Features

Chvac contains many, many advanced features. Here are just a few of its capabilities.

Calculation Method

Chvac performs cooling calculations using either the CLTD method or the new RTS (Radiant Time Series) method. The RTS method is described in the latest edition of the ASHRAE Handbook of Fundamentals, while the CLTD method is from earlier editions of the Handbook. The RTS method is especially accurate because it calculates the delayed effect of radiant heat gains during each of the past 24 hours in determining the current cooling load. That means, for example, that the program gives proper consideration to the effect of an external shading device that shades a window in the morning in a room that peaks in the afternoon. The CLTD method, on the other hand, uses exact table values from the Handbook where possible, which means that you can verify the results by hand. You can actually switch back and forth between RTS and CLTD for any project. All you have to do to switch between the two methods is to enter equivalent Master Data definitions for roofs, walls and glass and then change the Cooling Calculation Method input to the other method.

Program Input

Chvac is very easy to use and includes a specific "dropdown" help window for virtually every input, including a list of choices where appropriate. The program performs extensive checks on the data you enter and alerts you to any problems that it finds, such as a wall having too much window area, or a leaving coil temperature for an air handler outside of the expected range.

Five types of data are requested: general project data, outdoor design data, building material data, air handler data, and specific room data. The general project data includes the project and client name, designer, building opening and closing hours, internal operating load schedules, and any desired safety factors. The outdoor design data includes the summer and winter outdoor design conditions (automatically looked up for you if a city reference is given) 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. A user defined material library is available for saving the data on common material types. The air handler data includes the fan and terminal type, the desired heating and cooling supply air temperatures and data for duct heat gains and losses. The room data includes the room name, floor length and width, number of people, equipment watts, lighting watts, external shading data, and specific roof, wall, partition, floor and glass data.

Program Output

Chvac provides several different types of reports which can be selectively previewed on screen or printed. The reports are: General Project Data, Air Handler Input Data, Room Input Data, Detailed Project Room Loads, Air System Room Summary, Total Building, Air System, and Room Load Profiles, Air System Total Load Summary, Air System Psychrometric Analysis, Psychrometric Chart, Overall Building Envelope Report, Pie Charts, Bar Graphs, and the Total Building Load Summary. Virtually all calculated data can be exported to a comma delimited text file that you can then import into your favorite spreadsheet program such as Excel.

Chvac and HVAC Solution Link

The Chvac load calc program calculates a great deal of the data needed to define a system in the HVAC Solution schematic diagramming program. Traditionally, this data has simply been transferred using a manual entry process. Now, there is an automated process whereby HVAC Solution can import all the relevant Chvac data system by system into the HVAC Solution software such that HVAC schematic diagrams are automatically generated. See a video demo of this process here and view more details on HVAC Solution here.

Links to Other Programs

Chvac not only calculates peak heating and cooling loads, it also aids in selecting HVAC equipment and analyzing building operating costs. Project data from Chvac can be exported to Elite Software's Energy Audit program as well as to the eQUEST program (see more info in this paragraph). In the future, we plan to also provide a link to the Energy Plus program. Export to Energy Audit when you want to analyze residential and light commercial projects, essentially any application which uses unitary HVAC equipment. Export to eQUEST when you want to analyze large commercial projects that require precise modeling of variable loads, equipment, operating schedules, and control schemes. For just selecting unitary HVAC equipment, use the built-in Find HVAC Equipment feature of reading equipment performance databases published by the American Refrigeration Institute (ARI) and the Gas Appliance Manufacturers Association (GAMA).

Import and Export of gbXML Files

Chvac now lets you import gbXML files from CAD drawing software such as AutoCAD MEP and many other programs. We give you extensive control over the import process, including the ability to select which spaces, walls and windows to include in the import (see screenshot below). If you are familiar with the data that CAD programs typically write to gbXML files, you know that material definitions are usually incomplete for purposes of load calculation, since they do not usually include data such as wall U-values or roof ASHRAE numbers. So on the import dialog we let you select the default definitions for each kind of master material in the project.

Using eQUEST with Chvac for LEED Certification

Using the free eQUEST program with Chvac gives you a complete load calculation and energy analysis package. First, you enter your project in Chvac and let it determine your peak loads. Then, you export a ready-to-open eQUEST project file from Chvac. Then you open that project in eQUEST, and enter any additional data you want to enter that is specific to eQUEST. Then eQUEST will let you perform a detailed energy analysis. The eQUEST program can also be used to perform the calculations required for the energy portion of LEED certification, as described in an article in the September 2007 ASHRAE Journal (page 58 and following).

Drawing Board

A functional demo of Drawing Board is built into this version of Chvac. The built-in demo version of Drawing Board allows you to draw and save floor plans of unlimited size, but HVAC calculations can only be made for two rooms of the floor plan.

Update Information

Chvac version 7 users can update to version 8 for a substantial discount off the full purchase price. See the Upgrade Pricing page for more information.

New Features in Version 8

Chvac version 8 can be installed on the same computer as version 7, and will not interfere with version 7 at all. There is no problem in having both version 7 and version 8 on your computer at the same time.

The following new features were added to version 8 that were not in version 7.

New Features in Version 7

The following new features were added to version 7 that were not in version 6.

Screen shots


Comprehensive Air Handler Data

Runout and Main Trunk Duct Sizing

Built-in Custom and Favorite Material Lists

Easy Room Data Entry

All Types of Exterior Shading

Import and Export of gbXML Files

Drawing Board Window

Chvac includes a Drawing Board window, which operates at the demo level until you purchase a separate license for Drawing Board. The Drawing Board window enables you to enter your room data by simply drawing the floor plan on the screen. Below is a screen shot showing a floor plan created from within Chvac.

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