The project is a large mixed use complex which will include a high rise residential tower, a mid rise hotel, a theatre, retail base under each of the above 3 buildings and parking facilities associated with all of the above. The following important energy saving measures is being considered for a system which is 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 and will include engineered dryer exhaust systems to serve the stacked clothes dryers. In accordance with manufacturer\'s 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 exhaust system which will modulate the fan speed to maintain the recommended pressure in the riser at all times. We are also proposing to use a variable volume make-up air system which will vary the make-up air volume to match the exhaust flow rate. Both systems will substantially reduce fan energy and also reduce the required make-up air heating and cooling costs. ASHRAE 90.1 - 2004 does not address requirements for such dryer exhaust systems therefore we believe it is justified to model the baseline system as constant volume dryer exhaust with constant volume make-up air system. The proposed design will reflect the discussion above and be modeled as variable volume exhaust with variable volume recovery. Neither the baseline nor proposed design will include heat recovery because applicable codes prohibit any obstruction in the dryer exhaust systems. Please confirm whether modeling the baseline as constant volume exhaust and constant make-up without heat recovery and the proposed design as variable volume exhaust and variable volume make-up air without heat recovery is an acceptable modeling approach.
The project team is requesting verification of whether a variable volume exhaust system and variable volume make-up air system for stacked dryers in a residential building can be compared to a constant volume exhaust system in the Baseline energy model. As indicated by the project team, this issue is not addressed in ASHRAE 90.1-2004 prescriptive requirements or in Appendix G. Credit for systems not specifically addressed in the Appendix G modeling methodology must be modeled using the Exceptional Calculation Method, and theoretical and/or empirical information supporting the accuracy of the calculation method must be included. If the project submits an Exceptional Calculation Method to document credit for variable volume exhaust system and variable volume make-up air system for stacked dryers, they would need to clearly document: 1. That the Baseline system defined (including both the constant volume controls and fan capacities) is consistent with standard practice for similarly sized, newly constructed high-rise residential buildings. 2. How the control sequences will be applied to the project to achieve a true reduction in make-up air and exhaust-air volume during periods of low dryer usage (it is unclear how the pressure in the riser will correlate to the quantity of dryers in use, or how the makeup air and exhaust air volumes will be tracked with one another). Applicable Internationally.