Ben Larson 1 November th Avenue NE, Seattle, WA (206)

 SEEM: Simple Energy and Enthalpy Model  Used at the RTF and throughout the region to model energy use of residential buildings  The simulation currently has an energy balance and air moisture balance which predicts the annual heating and cooling energy requirements of a building  NEEA has funded development of an infiltration and ventilation module to SEEM 2

 Current SEEM uses a fixed value for the outside air infiltration to the house.  Input in ACHn (natural air changes per hour) & is constant every hour of year  Input value covers sources of outside air including infiltration and mechanical ventilation  Duct leakage impacts are calculated separately  Updated SEEM will calculate a different outside air infiltration amount for every hour of the year based on mass balance:  stack effect, wind, unbalanced duct leakage, and mechanically induced air flows.  New input will be CFM50Pa, the blower door test result of air leakage at 50 Pascals pressure difference  The user may input a fan schedule and airflow to interact with natural effects,  Additionally, internal gains can now be scheduled on an hourly basis (previously a user-set constant value) 3

 LBL (1980): Sherman and Grimsrud  Approach currently used in ASHRAE Stds  AIM-2 (1990): Walker and Wilson  Fundamentals the same across all models  Airflow through house described in set of non-linear equations  Implementations diverge  Computationally simple ▪ LBL and AIM-2 solve eqns with analytical approximations but with differing assumptions/implementations  Computationally intensive ▪ Ecotope model solves eqns numerically  leads to differing outcomes 4

 Building Parameters  Climate: Seattle  Stack height: 8.5’  CFM50: 1800 ▪ R: 0.5, X: 0 ▪ ¼ of leaks in floors, ▪ ¼ in ceilings, ▪ ½ in walls  Flow exponent: Hourly Infiltration Estimates for Stack and Wind Effects

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7  Sample calculations for a house with CFM50=2000, stack height=16 ft in a Seattle climate. Exhaust fan flow is continuous.  Solid lines calculated combined infiltration and exhaust flows using full model  Dashed lines combined infiltration and exhaust flows using Palmiter/Bond ½ rule.

 Houses with ventilation systems which operate on an hourly level can now be modeled  Infiltration now more accurately modeled over the entire year  More infiltration under strong heating and cooling conditions and less in the shoulder seasons  Energy impacts of ventilation codes/stds, such as ASHRAE 62.2 can be modeled  Interior installations of heat pump water heaters  combining a ventilation and internal gains schedule can model both vented and unvented scenarios 8

 What do we mean when we say a house has 0.35ach? (effective annual average outside air changes)  To get to 0.35ach, if the blower door test is 7ach50, the annual effective air change will also include mechanical sources  Without mechanical sources, the natural infiltration implied by a 7ach50 test, gives effective annual ach depending on building type and climate. ▪ “divide by ___” rule of thumb for converting BD test to ach natural  New infiltration model allows (requires) us to understand (assign) separate sources of outside air: ▪ stack, wind, ducts, mechanical ventilation  Potential implications for weatherization and sealing measures 9