The project is a large mixed use complex which will include a high rise residential tower, a mid rise hotel, a theater, retail base under each of the above 3 buildings and parking facilities associated with all of the above. There are several energy saving measures being considered for systems which are not addressed in ASHRAE 90.1-2004 prescriptive requirements or appendix G. Please advise if the proposed approach to modeling is acceptable. 1. The high rise residential tower includes provisions for individual clothes dryers in each apartment. Thus the building will include engineered dryer exhaust systems to serve the stacked clothes dryers. In accordance with manufacturers recommendations and good engineering practice, the exhaust systems will be sized based on a 60% diversity factor to be able to function during periods of high usage. Typically such systems are constant volume systems that exhaust air continuously, even when most of the dryers are off. We are proposing to use a variable volume system which will modulate the fan speed to maintain the recommended pressure in the riser at all times. This will substantially reduce fan energy and also reduce the required make-up air heating and cooling costs, since the make-up air unit will be VAV and reduce volume in proportion to the reduction in dryer exhaust volume. ASHRAE 90.1 - 2004 does not address requirements for such systems therefore we believe it is justified to model the baseline system as constant volume exhaust with corresponding constant volume make-up air. The make-up air unit also includes capacity to match the toilet exhaust. However the toilet exhaust is less than the dryer exhaust and makes up only about 40% of total exhaust. We propose to provide heat recovery from the toilet exhaust to the make-up air. We believe that the baseline model can be set up without heat recovery from the toilet exhaust based on the fact that the system meets exception 6.5.6.1 (h) where the largest exhaust source is less than 75% of the design outdoor airflow and thus is not required to have heat recovery. 2. The lower level parking garage is classified as enclosed and thus mechanically ventilated. The parking garage serves the hotel and residential building and thus will be in use 24 hours a day. We are proposing to provide a system of carbon monoxide sensors and associated controls to operate the ventilation for areas of the garage only as needed to maintain
Three proposed modeling approaches have been described in this request. 1. The project team proposes to model the baseline case toilet exhaust without heat recovery. This approach is not acceptable. Sub-section (f) under ASHRAE 90.1-2004 Section G3.1.2.10 (f) states that "this exception shall only be used if exhaust air recovery is not used in the proposed design." While Section 6.5 is a mandatory section for the purposes of meeting EAp2; modeling guidelines should be followed as per ASHRAE 90.1-2004, Appendix G. 2. The project team proposes modeling the parking garage ventilation system as variable, dependent on carbon monoxide sensor readings and the baseline case as constant. This is acceptable, but should be modeled as an exceptional calculation method if automatic controls cannot be explicitly modeled using the approved energy modeling software. Documentation must be provided that supports the savings and assumptions made if using an Exceptional Calculation Method. Please refer to ASHRAE 90.1-2004 Section G2.5 for further guidance. 3. The project team proposes that heat recovery does not have to be modeled in the baseline case for a central boiler plant/transformer vault ventilation system. This approach is acceptable, given that the air is tempered to 50