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 zone 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.

• Calculates Peak Heating & Cooling Loads
• Determines Building Tonnage and Room CFM Requirements, and Runout Duct Sizes
• Uses either the RTS or CLTD calculation method
• Computes CFM Air Quantities With Psychrometrics
• Calculates from Manually Entered Data or Directly from Floor Plans Created with Drawing Board (sold separately)
• Links with Elite Software's Energy Audit and EZDOE Energy Programs
• Transfers data to the eQUEST and PowerDOE Energy Analysis Programs
• Allows 30 Walls, 30 Windows, and 12 Roofs per Zone
• Automates Compliance with ASHRAE Standard 62
• Calculates in both Metric and English Units
• Converts any project from English to Metric units and vice-versa
• Allows Simultaneous Infiltration and Ventilation
• Calculates Runout and Main Trunk Duct Sizes
• Selects Equipment from ARI/GAMA Databases
• Allows Virtually Unlimited Number of Zones
• Zones May be Optionally Grouped Under VAV Boxes
• Prints Numerous Color Pie Charts and Bar Graphs
• Creates Spreadsheet Output File
  

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

• Calculates Peak Heating and Cooling Loads
• Calculates Both Heating & Cooling CFM Requirements
• Calculates Runout and Main Trunk Duct Sizes
• Automates Compliance with ASHRAE Standard 62
• Provides Overall Building Envelope Report
• Creates Spreadsheet File with Calculated Results
• Performs Complete Psychrometric Analysis
• Prints Bar Graphs and Exploded Pie Charts
• Exterior Shading Handles Overhangs, Fins, & Glass Tilt
• Uses Exact ASHRAE RTS or CLTD Procedures
• Built-in Design Weather Data for Hundreds of Cities
• Analyzes Up to 12 Months Per Calculation
• Calculates 24 Hours per Design Day
• Allows Unlimited Number of Zones per Project
• Zones May Be Grouped Under 100 Air Handlers
• Zones May Be Optionally Grouped Under VAV Boxes
• Allows 30 Walls, 30 Windows, and 12 Roofs per Zone
• Allows Simultaneous Infiltration and Ventilation
• Allows Different Summer and Winter Air Rates
• Allows Varying Indoor Conditions Within a Project
• Allows 20 Master Roof Types, 20 Master Wall Types, 20 Master Partition Types, and 50 Master Glass Types
• Provides a User-Defined Library of Custom Materials
• Provides a List of your Favorite Materials
• Allows Up to 10 Internal Operating Load Profiles
• Allows Full 360 Degree Wall and Glass Orientations
• Allows Glass to be titled from 0 to 180 degrees
• Allows for Roof and Wall Color Effects
• Provision for Both VAV and Constant Volume Systems
• Proper Handling of Return Air Plenum Loads
• Accounts for People Diversity in Total Building Load
• Computes Supply Fan Horsepower and Heat Gains
• Accounts for Both Draw-thru and Blow-thru Fans
• Calculates Reheat Requirements if Necessary
• Computes Supply and Return Duct Gains and Losses
• Allows Direct Specification of Supply CFM Quantities
• Allows Specification of Minimum Supply Air Quantities
• Allows Heating Only, Cooling Only, or Both
• Excess Supply Air Can be Handled as Reheat, Reserve Capacity, or by Adjusting the Leaving Coil Conditions
• Leaving Coil Conditions Can be Specified with a Desired Dry Bulb Temperature or a Relative Humidity
• Calculates Chilled and Hot Water Coil Flow Rates
• Allows for Pretreated Outside Air
• Allows Heating and Cooling Safety Factors
• Lighting & Equipment Watts along with No. of People can be Entered Directly or on a Per Square Foot Basis
• Selects Equipment from the ARI/GAMA Databases
• Creates Custom Sales Proposals
• Creates Spreadsheet Output File
  

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 zone 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 zone 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 zone data includes the zone 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, Zone Input Data, Detailed Project Zone Loads, Air System Zone Summary, Total Building, Air System, and Zone 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.

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 and EZDOE programs as well as to the eQuest and PowerDOE programs (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 EZDOE, eQUEST, or PowerDOE 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 ).

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 zones of the floor plan.

Update Information

Chvac users with earlier versions can update to version 7 for a substantial discount off the full purchase price (to go from version 6 to 7 is $149). If you have Chvac version 6.01 through 6.04 it is VERY IMPORTANT that you first download and install the final revision of 6.04 before installing version 7. The final version of 6.04 includes changes that prevent you from mistakenly opening a project file in the wrong version of the program.

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

• RTS Calculation Method: You can now select to use either the CLTD method or the new Radiant Time Series (RTS) method for calculating cooling loads. The RTS method is found in the latest ASHRAE Handbook of Fundamentals and is very accurate because it calculates the delayed effect of radiant heat gains during each of the past 24 hours on the current cooling load. You can easily switch back and forth between the two methods simply by entering equivalent master roof, wall and glass data on the Master Data window for both methods.
  
  
• Easier and Better Glass Definitions: Now you can enter the width and height dimensions for each window or skylight rather than having to enter them for the master glass and then figure out the correct quantity to enter on the Zone Data window. The Room Construction value of Light, Medium or Heavy required for each glass in the CLTD method is now automatically assigned based on the selection you make for the entire zone in the new Zone Type input.
  
  
• Individual Ground Reflectance Values: You can enter a different ground reflectance for each component rather than having only one value for the whole project, which makes the results more accurate because different exposures around a building are likely to have different ground reflectances. Because the RTS method requires this input for roofs and walls, each roof and wall now has a Ground Reflectance input, which makes it so each skylight and window is automatically assigned a ground reflectance value that is appropriate for its exposure.
  
  
• Glass Number of Occurrences: You only have to enter data once for a window or skylight that occurs multiple times in the same wall or roof.
  
  
• Floor Slab Coefficient for Each Zone: You can now enter the floor slab coefficient for each zone rather than having to use the same value for the whole project.
  
  
• Easier to Use Zone Data Window: The Zone Data window has been redesigned to make it easier to enter all the data. You can change the number of visible roofs, walls and glass by clicking the plus and minus buttons next to each group's scrollbar. Pressing Enter when on the last visible row of a component now makes the components scroll down by one so you can enter another item of the same type. If the Type input of a component is set to zero, pressing Enter moves the cursor to the next group of inputs. All the important data is now on two tabs instead of three.
  
  
• More Roofs, Walls and Glass per Zone: We've more than doubled the allowed number of roofs, walls and glass you can enter for a zone.
  
  
• Zone Notes: You can save as many notes about a zone as you want in the new "Notes About This Zone" input on the Zone Data window.
  
  
• Easier Weather Data Selection: Both the Weather Database and the Indoor/Outdoor Design windows now let you select a city from a single dropdown list that shows all cities in the database.
  
  
• Easier Weather Database Editing: It is now much easier to edit and add cities in the redesigned Weather Database window.

Comprehensive Air Handler Data

Runout and Main Trunk Duct Sizing

Drawing Board Window