8.7   HVAC Issues

8.7.1    No Cooling Installed

When a building does not have a proposed cooling system, there is no compliance credit. The air conditioning system is modeled to be equivalent to Package A. A hypothetical cooling duct system is modeled as equivalent to Package A (e.g., Attic, R-6) or as matching the heating system ducts. Modeling no ducts is not an appropriate assumption.

8.7.2    Equipment without SEER or HSPF

For equipment without a tested SEER, the EER is used in place of the SEER. Another option is to use the EER of the equipment and use it for both the SEER and EER entry. If this approach is used, the EER must be verified by a HERS rater.

Equipment without an HSPF rating is assumed to have 3.41 HSPF (electric resistance), 3.55 (electric radiant), or an HSPF calculated from a COP as

HSPF = (3.2 x COP) – 2.4.

8.7.3    Multiple HVAC Systems

Buildings with multiple HVAC systems can be treated in a couple of different ways as follows:

      For buildings that have more than one system type, equipment type or fuel type, where the types do not serve the same floor area, model either the building zone or enter the floor area served by each zone type.

      When multiple system types serve different thermal zones in one building, model each system and its associated thermal zone separately from other systems and zones.

Note that if both zones are associated with attic space then a portion of the attic must be modeled with each zone.

      Floor areas that are served by more than one heating or cooling system, equipment type, or fuel type must be modeled for compliance using the system with the most TDV energy consumption. For any areas served with electric resistance heat and another heating system (except for wood heating) the electric resistance shall be deemed to be the most TDV energy consuming system. The only exceptions to this are supplemental heating units may be installed in a space served directly or indirectly by a more efficient primary heating system. This is allowed if the thermal capacity of the supplement unit does not exceed two kilowatts or 7,000 Btu/h and is if the supplemental unit is controlled by a time-limiting device not exceeding 30 minutes. See §150.1(c)8C.

When there is more than one system meeting the heating or cooling load for the same space, all systems must still meet all the mandatory requirements of the standards.

For example, in a building with an appliance rated gas fireplace in combination with a central gas furnace, the central furnace would be used as the primary system and the fireplace would be treated as the supplemental system. The controls for the fireplace would not need to meet the setback thermostat requirements of §110.2(c) due to the exception.

For rooms such as the bedroom or bathroom, spot heating with a supplemental system may be desirable. Exception to §150.1(c)6 is provided for installing either a two kW electric resistance or 7,000 Btu gas heaters, with a 30-minute timer control for such instances. Therefore, this type of supplemental space heating need not meet the setback thermostat requirement.

8.7.4    Existing + Addition + Alteration Approach

The performance approach may be used to show compliance for alterations in existing buildings, new additions, and Existing + Addition + Alteration discussed in Section 9.7 of this 'manual.