We are requesting clarification regarding what percentage of a building must be open 24 hours for the building to be considered a 24-hour facility. ASHRAE 90.1-2004, Section 6.5.6.2 requires condenser heat recovery for preheating service hot water for facilities operating twenty-four hours per day, when the total installed heat rejection capacity of the water-cooled systems servicing the building exceed 6,000,000 Btuh, and the design service water heating load exceeds 1,000,000 Btu/h. Our project is a large retail complex which most likely exceeds the total installed heat rejection and service water heating loads listed. However, only 17% of the complex (a large arcade facility) is open 24 hours per day. The rest of the complex will be closed for a portion of each day. We believe we are exempted from the heat recovery requirement since the domestic water heating loads are mostly coming from the areas of the building that are not open 24 hours, and since only a fraction of the complex is open 24 hours per day. We would like confirmation that our interpretation is correct.
The applicant is asking to confirm their interpretation of a specific ASHRAE 90.1-2004 requirement. Based on the description provided, if the project is served by a single system, it should be considered as a 24 hour facility. If the system used for the conditioning of only the 17% of the complex (open as a 24 hour facility) does not meet the heat rejection or service water heating requirement, it would be exempt from the requirements of ASHRAE 90.1-2004, Section 6.5.6.2. Table G3.1 section 11 of ASHRAE 90.1-2004 describes the modeling requirements for service water heating systems including those covered by ASHRAE 90.1-2004, Section 6.5.6.2.