Use the "Browse" button to locate the AkWarm file on your computer you wish to perform the Design Heat Loss calculation on. If you do not have an AkWarm file available, but wish to evaluate the software, click on the downloading a sample AkWarm file here link. Save the AkWarm file to your computer. Then use the "Browse" button to retrieve the file to the AkWarm Design Heat Loss Program. Once you have located the file with the Browse button, simply double click on the file, or click once on the selected AkWarm file and then click the "Open" button.
The name of the file should appear in the AkWarm File Box. Click on the "Next Step" button to proceed. The Step 2 screen will provide you with the AkWarm file name and address of the home. If this is the correct AkWarm file, proceed by clicking on the "Next Step".
The Design Heat Loss Report will include the operator name if one is provided in the Operator Name field. This name may be different than the person who generated the AkWarm Energy Rating file.
Indoor Temperature: The indoor temperature is defaulted to 70 F. The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) residential energy standard recommends a design indoor temperature of 70 F. A higher indoor temperature will result in a larger design heat load. Users should be cautioned to avoid "padding" design temperatures and wind speed inputs as a way to provide a safety margin. A separate System Sizing Safety Margin input is provided for the user to include a reasonable overall safety margin in the Design Heat Loss calculation.
Outdoor Temperature: The design outdoor temperature default is from the AkWarm weather database for the community selected or the closest available weather station. Outdoor temperatures can vary significantly in and around communities. The Design Outdoor Temperature is not the coldest recorded temperature. It is not prudent to consider the most extreme recorded temperature when sizing a heating system. ASHRAE recommends a 97 ½ percentile temperature for use in calculating Design Heat Load. Local weather service or code officials may have more appropriate design outdoor temperatures for the area. Users should be cautioned to avoid "padding" design temperatures and wind speed inputs as a way to provide a safety margin. A separate System Sizing Safety Margin input is provided for the user to include a reasonable overall safety margin in the Design Heat Loss calculation.
Garage Temperature: The indoor garage temperature is defaulted to 55 F. A higher indoor garage temperature will result in a larger design heat load for the garage. Depending upon the construction of adjoining walls and ceilings, cold garage indoor temperatures may not be recommended due to moisture and foundation issues. Users should be cautioned to avoid "padding" design temperatures and wind speed inputs as a way to provide a safety margin. A separate System Sizing Safety Margin input is provided for the user to include a reasonable overall safety margin in the Design Heat Loss calculation.
Site Wind Speed: The site wind speed is calculated from the AkWarm weather database using local airport average wind speed for December. The wind speed then is adjusted downward depending upon the wind shielding and height of the building. The site wind speed affects the air infiltration and the insulation values of above-grade building components. Increasing the site wind speed will increase the design heat load of the home. Note: For most communities, site wind speeds at design outdoor temperature conditions are generally near or at zero.
Mechanical Ventilation Rate for Home, Supply Flow: Enter the supply flow rate, in cubic feet per minute (cfm), of the home's mechanical ventilation system, if present. The program accepts an input for both the supply and exhaust flow rates of the system. The exhaust flow input follows this input. For balanced ventilation systems, such as HRVs, the supply and exhaust flow rates should be the same. For unbalanced systems the supply and exhaust flow rates differ. For example, if the ventilation system is a 100 cfm exhaust-only system, you would enter 0 cfm for the supply flow rate and 100 cfm for the exhaust flow rate.
The effective ventilation rate at design heating conditions is a combination of natural air leakage and mechanical ventilation. The Design Heat Loss Program calculates the natural air leakage rate at design outdoor temperature and site wind speed based upon the estimated or actual blower door test results provided in the AkWarm file. The Mechanical Ventilation Rate for the home, if any, is in addition to the natural air leakage. Because of the increased natural air leakage during design outdoor temperatures, operation of continuous ventilation systems can result in unacceptable low indoor humidity levels and are therefore generally not run continuously, or at the higher flow rate settings. The required amount of ventilation to achieve a 0.35 air change rate (ACH) is provided as a default input value. Also, this value is provided in the Notes below the Input box as a reference, based upon ASHRAE ventilation standards for homes.
Note: The program automatically accounts for the reduced effectiveness of unbalanced ventilation systems, such as exhaust-only. These systems provide less ventilation than indicated by their operating flow rate.
Mechanical Ventilation Rate for Home, Exhaust Flow: Enter the exhaust flow rate, in cubic feet per minute (cfm), of the home's mechanical ventilation system, if present. The program accepts an input for both the supply and exhaust flow rates of the system. The supply flow input precedes this input. For balanced ventilation systems, such as HRVs, the supply and exhaust flow rates should be the same. For unbalanced systems the supply and exhaust flow rates differ. For example, if the ventilation system is a 100 cfm exhaust-only system, you would enter 0 cfm for the supply flow rate and 100 cfm for the exhaust flow rate.
The effective ventilation rate at design heating conditions is a combination of natural air leakage and mechanical ventilation. The Design Heat Loss Program calculates the natural air leakage rate at design outdoor temperature and site wind speed based upon the estimated or actual blower door test results provided in the AkWarm file. The Mechanical Ventilation Rate for the home, if any, is in addition to the natural air leakage. Because of the increased natural air leakage during design outdoor temperatures, operation of continuous ventilation systems can result in unacceptable low indoor humidity levels and are therefore generally not run continuously, or at the higher flow rate settings. The required amount of ventilation to achieve a 0.35 air change rate (ACH) is provided as a default input value. Also, this value is provided in the Notes below the Input box as a reference, based upon ASHRAE ventilation standards for homes.
Note: The program automatically accounts for the reduced effectiveness of unbalanced ventilation systems, such as exhaust-only. These systems provide less ventilation than indicated by their operating flow rate.
Ventilation Heat Recovery Effectiveness: This input is for heat recovery ventilation systems (hrv's). All non-heat recovery ventilation systems should be set to zero. The default value for heat recovery ventilation system effectiveness is 0.75. A more accurate value can be obtained from the hrv manufacturer energy performance testing report for "Apparent Sensible Effectiveness." Most hrv's test reports are listed in the Home Ventilating Institute (HVI) CERTIFIED HOME VENTILATING PRODUCTS DIRECTORY. Note: Input must be in a decimal format, for example: 78% = 0.78
House/Garage Uninsulated Common Area: Heat flow from the house through uninsulated common walls and ceilings into a cooler garage increases the design heat load for the house and decreases the heat load for the garage. The amount of heat transfer between the house and garage will depend on the total uninsulated areas common to the house and garage, and the indoor temperature difference between the house and garage. Do not include any common areas that are insulated. Setting the garage design indoor temperature at the same design indoor temperature for the house will result in zero heat flow between the house and garage.
Main Home Heating System Distribution Efficiency: Distribution heat losses from poorly insulated pipes and ducting in unconditioned space, forced-air duct air leakage to outside, and increased natural air leakage from pressure imbalances in the home, all contribute to the design heat requirements. Hydronic heating systems with all piping within conditioned space is assumed to have little or no distribution losses and should be set at 100% (1.0). Distribution efficiency for forced-air furnace systems is difficult to quantify. New construction with properly sealed ducts and balanced supply and returns should be assumed to be 95% - 100% (.95 - 1) efficient. Forced-air furnaces with significant duct leakage and/or pressure imbalances within the home may be only 85% - 95% efficient in delivering the heat from the furnace to the house. (Some of the increased air leakage may be offset by reduced mechanical ventilation flow rates.) Users should be cautioned to avoid unnecessary "padding" of distribution efficiencies as a way to provide additional safety margin. A separate System Sizing Safety Margin input is provided for the user to include a reasonable overall safety margin in the Design Heat Loss calculation.
System Sizing Safety Margin, Home: The less you know about the construction of a home the more uncertain your assumptions may be regarding design heat load requirements. The detailed surface areas and R-values provided by the AkWarm house file, along with air tightness testing, provide for reasonably accurate estimate of the design heat load of a home. Additional safety margins not included in this design heat load calculation include internal gains from refrigerators, freezers, lighting, fans, pumps, etc., domestic hot water usage, and occupants. These internal gains can reduce the actual design heat load by 5% to 10%. Supplemental heat sources in the home, such as, vented gas fireplaces or wood stoves also reduce the need for safety margins.
Unnecessary over-sizing of space heating equipment reduces efficiency and comfort control, while increasing installation, operating and maintenance costs. A 20% (.20) Safety Margin is used for a default value. Homes with supplemental heat can have less of a Safety Margin, while older existing homes with less certainty regarding insulation values and air tightness may warrant a slightly higher Safety Margin.
Mechanical Ventilation Rate for Garage: The effective ventilation rate at design heating conditions is a combination of natural air leakage and mechanical ventilation. The Design Heat Loss Program estimates the natural air leakage rate at design outdoor temperatures for the garage based upon the estimated or actual blower door test results provided in the AkWarm file. The Mechanical Ventilation Rate for the garage is, if any, in addition to the natural air leakage. Note: Unbalanced ventilation systems, such as exhaust only, do not increase ventilation by their operating flow rate. ASHRAE 136 provides a method of determining the combined effect of mechanical and natural air leakage based upon local weather factor and building tightness. In general, roughly only ½ of the airflow out an exhaust fan is contributing to the ventilation rate. For example a 100 cfm exhaust fan will only provide approximately 50 cfm of mechanical ventilation when combined with the natural air leakage rates. In addition, any flow of air from the house into the garage will not need heating within the garage, but may increase the ventilation rate in the home.
Garage Heating System Distribution Efficiency: Distribution heat loss from poorly insulated pipes and ducting in unconditioned space, forced-air duct air leakage to outside, increased natural air leakage from pressure imbalances in the home, all contribute to the design heat requirements. Hydronic heating systems with all piping within conditioned space is assumed to have little or no distribution losses and should be set at 100% (1.0). Radiant floor heated slabs with little or no perimeter insulation will have higher heat losses than predicted and can be adjusted accordingly by lowering the distribution efficiency 5% - 10%. Hydronic and air unit heaters are assumed to have no distribution losses.
System Sizing Safety Margin, Garage: The less you know about the construction of a garage the more uncertain your assumptions may be regarding design heat load requirements. The detailed surface areas and R-values provided by the AkWarm house file, along with air tightness testing, provide for reasonably accurate estimate of the design heat load of a garage. Additional safety margins not included in this design heat load calculation include internal gains from refrigerators, freezers, lighting, fans, pumps, domestic hot water and boiler standby losses, heat flow from the house into the garage. In addition, garages typically are not occupied for any length of time so that any loss of comfort by not being able to maintain the design indoor temperature will be minimal.
This field allows the operator to include any comments regarding the condition of the home, deviations from the default inputs, etc… The notes will be printed out in the Design Heat Loss Report.
If you have additional questions, please e-mail the questions by clicking this link.