This credit interpretation request is in reference to the modeled baseline HVAC system. The project is a 142,000 sqft health care facility to be built in Northern Italy. Two questions arise due to the location and use of the building. 1) The pressurization and air change requirements of a health care facility meet exception (c) of G3.1.1 which indicates System 3 - PSZ-AC is to be used as the baseline system. A single zone constant volume system is unable to adequately meet the temperature and humidity control requirements without reheat and would not be used in this type of facility. Omitting the reheat capabilities of the baseline system puts the design model at an extreme disadvantage when comparing energy use and does not seem to meet the intent of the standard. It is proposed that for this project reheat also be included in the baseline model to account for the temperature and humidity control requirements of a health care facility. 2) Italian health care facilities require substantial fan energy due to high air change rates, AHU components and duct accessories compared to other facilities such as office buildings. The intent of this section 3.1.2.9 was to enable credit for and encourage more efficient fan systems. The only pressure credit given is for systems requiring filtering systems in excess of 1 in. w.c. static pressure. Air pressure drops associated with cooling coils, preheat coils, multiple filter stages, air blenders, extensive sound attenuation required by Italian law, humidifiers, exhaust bio-safety cabinets, and excessive number of fire and smoke dampers due to Italian law all contribute to the excessive fan energy required. It is proposed this calculation not be used to penalize the design model for meeting Italian health care facility requirements and to determine the baseline system fan power on the same static pressure as the proposed design. Great effort was put forth to provide an energy efficient HVAC design while meeting or exceeding the design requirements. Both of the issues stated penalize this effort and therefore would not be the intent of the standard.
The project team is requesting direction regarding energy modeling of HVAC systems for a health care facility. Two issues are raised; humidity control and fan power characteristics. These parameters can vary substantially from a typical office building and as indicated by this CIR, the 2004 version of Appendix G has some limitations when addressing health care facilities. Regarding the first issue, this CIR states that a single zone, constant volume system is unable to meet temperature and control requirements without reheat. This is true, and is an issue for any application that has humidity control requirements (such as a telecom or server room). ASHRAE 90.1-2004 Table G3.1 Proposed (b) states that temperature and humidity control setpoints shall be the same for the proposed and baseline building designs. The design team should follow the Appendix G requirements and model those spaces with pressurization control requirements with System 3 -PSZ-AC in the baseline building. Humidity control requirements should be the same as in the proposed building, even if that requires reheat to be modeled with that system type. The second issue; fan power is not adequately addressed by the 2004 version of Standard 90.1 for healthcare and laboratory applications. Addendum ac to Standard 90.1, and related changes to Appendix G have been adopted by ASHRAE, and will be published in the 2007 version of the Standard. These changes specifically address the issues raised by the project team, and may be used for this project. Included in Addendum ac are added pressure drop credits for fan systems that include evaporative cooling, sound attenuation, ducted returns, filtration, and return or exhaust airflow control devices. These credits are contained in TABLE 6.5.3.1.1B of addendum ac. The corresponding changes to Appendix G were not published with Addedum ac, but are reproduced below. The changes to Appendix G as well the requirements of Addendum ac may be used by the applicant. ********************************************************************************************************* G3.1.2.9 Supply Fan Power. System fan electrical power for supply, return, exhaust, and relief (excluding power to fan-powered VAV boxes) shall be calculated using the following formulas: For Systems 1 and 2 Pfan = CFMS * 0.3 For Systems 3 through 8 Pfan = bhp x 746 / Fan Motor Efficiency where Pfan = electric power to fan motor (watts) and bhp = brake horsepower of baseline fan motor from Table G3.1.2.9 Fan Motor Efficiency = the efficiency from Table 10.8 for the next motor size greater than the brake horsepower using the Enclosed Motor at 1800 RPM CFMS = the baseline system maximum design supply fan air flow rate in cubic feet per minute TABLE G3.1.2.9 Baseline Fan Brake Horsepower Baseline Fan Motor Brake Horsepower Constant Volume Systems 3 - 4 // Variable Volume Systems 5 - 8 CFMS * 0.00094 + A // CFMS * 0.0013 + A Where A is calculated according to 6.5.3.1.1 using the pressure drop adjustment from the proposed building design and the design flow rate of the baseline building system. Do not include pressure drop adjustments for evaporative coolers or heat recovery devices that are not required in the baseline building system by Section G3.1.2.10.