Safety Factors
- Room/Space Peak Loads 1.1 × Calc. Load
- Floor/Zone Loads (Sum of Peak) 1.0 × Calc. Load
- Floor/Zone Loads (Block) 1.1 × Calc. Load
- Building Loads (Sum of Peak) 1.0 × Calc. Load
- Building Loads (Block) 1.1 × Calc. Load
- Generally: Sum of Peak Loads = 1.1 × Block Loads
Heating Load Credits
- Solar. Credit for solar gains should not be taken unless building is specifically designed for solar heating. Solar gain is not a factor at night when design temperatures generally reach their lowest point.
- People. Credit for people should not be taken. People gain is not a factor at night when design temperatures generally reach their lowest point because buildings are generally unoccupied at night.
- Lighting. Credit for lighting should not be taken. Lighting is an inefficient means to heat a building and lights are generally off at night when design temperatures generally reach their lowest point.
- Equipment. Credit for equipment should not be taken unless a reliable source of heat is generated 24 hours a day (i.e., Computer Facility, Industrial Process). Only a portion of this load should be considered (50%) and the building heating system should be able to keep the building from freezing if these equipment loads are shut down for extended periods of time. Consider what would happen if the system or process shut down for extended periods of time.
Heating System Selection Guidelines
- If heat loss exceeds 450 Btu/Hr. per lineal feet of wall, heat should be provided from under the window or from the base of the wall to prevent downdrafts.
- If heat loss is between 250 and 450 Btu/Hr. per lineal feet of wall, heat should be provided from under the window or from the base of the wall, or it may be provided from overhead diffusers, located adjacent to the perimeter wall, discharging air directly downward, blanketing the exposed wall and window areas.
- If heat loss is less than 250 Btu/Hr. per lineal feet of wall, heat should be provided from under the window or from the base of the wall, or it may be provided from overhead diffusers, located adjacent to or slightly away from the perimeter wall, discharging air directed at or both directed at and directed away from the exposed wall and window areas.
ASHRAE Standard 90.1
- Pick-Up Loads 30% Maximum System Capacity Allowance for Morning Warm-Up Cycles
- Safety Factor 10% Maximum
FREQUENTLY ASKED QUESTIONS
The selection of a safety factor depends on various factors, including the building’s occupancy schedule, climate, and construction type. ASHRAE Standard 90.1 provides guidelines for safety factors, which range from 1.0 to 1.1, depending on the type of load and the level of uncertainty. For example, a safety factor of 1.1 may be used for room space peak loads, while a safety factor of 1.0 may be used for building loads. It’s essential to consult with local building codes and regulations to determine the appropriate safety factor for your specific project.
Heating load credits refer to the reduction in heating load due to internal heat gains from sources such as solar radiation, people, lighting, and equipment. These credits are subtracted from the total heating load to determine the net heating load. However, it’s essential to note that these credits should only be taken if the building is specifically designed to utilize these heat gains, such as through passive solar design or high-efficiency lighting systems. Otherwise, these credits should not be applied to avoid oversizing the heating system.
No, solar gains should not be taken as a credit in heating load calculations unless the building is specifically designed for solar heating. Solar gain is not a reliable source of heat, as it is only available during the day and is affected by factors such as cloud cover and shading. Moreover, solar gain is not a factor at night when design temperatures generally reach their lowest point. Therefore, it’s recommended to ignore solar gains when calculating the heating load to ensure that the heating system is sized to meet the maximum heating demand.
ASHRAE Standard 90.1 provides guidelines for heating load calculations, including requirements for safety factors, heating load credits, and system sizing. The standard recommends using a comprehensive approach to heating load calculations, taking into account various factors such as climate, occupancy, and building construction. By following ASHRAE Standard 90.1 guidelines, HVAC designers can ensure that their heating systems are designed to meet the minimum energy efficiency requirements and provide a comfortable indoor environment for building occupants.
Oversizing a heating system can lead to several negative consequences, including increased energy consumption, higher capital costs, and reduced system efficiency. An oversized heating system can also lead to short cycling, which can reduce the system’s lifespan and increase maintenance costs. Furthermore, an oversized system may not provide the desired indoor comfort, as it may cause overheating or uneven heating. Therefore, it’s essential to perform accurate heating load calculations to ensure that the heating system is sized correctly and operates efficiently.
The selection of a safety factor depends on various factors, including the building’s occupancy schedule, climate, and construction type. ASHRAE Standard 90.1 provides guidelines for safety factors, which range from 1.0 to 1.1, depending on the type of load and the level of uncertainty. For example, a safety factor of 1.1 may be used for room space peak loads, while a safety factor of 1.0 may be used for building loads. It’s essential to consult with local building codes and regulations to determine the appropriate safety factor for your specific project.
