Michael Logsdon, Ben Larson, David Baylon 13 December 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  Under a NEEA project, Ecotope has developed of an infiltration and ventilation module, an air mass balance, for SEEM 2

 Changes to SEEM  Natural infiltration sources  Calculating infiltration due to natural & mechanical sources  SEEM specific modeling assumptions  Example infiltration model output  Comparison to other infiltration models  Comparison to field measurements  Discussion 3

 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 includes sources of outside air: infiltration & mechanical ventilation  Duct leakage impacts are calculated separately  Updated SEEM calculates a different outside air infiltration amount for every hour of the year based on mass balance:  stack effect, wind, mechanically inducted airflows, and both balanced and unbalanced duct leakage  Key new inputs: ▪ CFM50Pa: the blower door test result of air leakage at 50 Pascals pressure difference ▪ Stack height: average height of a column of warm indoor air above grade ▪ Fan flows and schedules  Additional updates: hourly schedules for internal gains and thermostat settings 4

 Inputs:  CFM50  Stack Height  Fan Type (Exhaust, Supply, HRV)  Fan CFM  Fan Efficiency or HRV Efficiency  Schedules: Fan, T-Stat, Internal Gains ▪ Schedules are hourly & include 7 individual days per week  Outputs:  Average Annual ACH  Ventilation Fan Energy (kWh/yr to run ventilation system)  Balance Point 5

 Natural Infiltration: airflow caused by pressure differences across cracks and leaks  Total infiltration: airflow caused by the cumulative effects of natural infiltration and mechanical ventilation.  The model does not account for occupant effects such as opening doors or windows. 6

Driving Force: ΔT 7 Driving Force: Wind Speed

Empirical Power Law Flow: Q=CΔP n  Q – Flow rate, typically Cubic Feet per Minute (CFM)  C – Constant with units CFM/(Pascals^n)  ΔP – Pressure difference  n – Dimensionless flow exponent 8 Rewrite equation to define a “leakage area”

 Inflows are positive, outflows are negative, and all flows must sum to zero: Mass is neither created nor destroyed in this process.  Flow through the floor, walls, and ceiling depend on pressure difference as found from stack effect and wind.  Mechanical flow is the net, unbalanced flow rate due to mechanical sources, such as exhaust fans, unbalanced duct leakage, etc… 9

 Flow Exponent n=0.65 Leakage Area Distributions Crawlspace Floor: 25% Walls: 50% Ceiling: 25% Slab/Heated Basement Floor: 0% Walls: 67% Ceiling: 33% 10

 Average value of flow exponent from Modeled & Measured Infiltration Papers is (sample size = 10)  Blower Door User Manual suggests using n=0.65 as a typical flow exponent for large sample sets  In progress RBSA dataset 11

 Houses are Square  Wind acts only on the walls  Wind approaches either orthogonal to a face or at a 45° angle  Leakage area is distributed uniformly along the walls 12

Velocity is found according to the AIM-2 method  Meteorological wind speed is corrected to site wind speed 13  Vsite is further reduced for local shelter to Veffective  Assume Shelter Class 3 “Heavy shielding, many large obstructions within two house heights with Sw=0.7.

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Annual average ACH Method ClimateSEEMAIM-2LBL62.2 Seattle, WA Portland, OR Boise, ID Spokane, WA Kalispell, MT  Sample calculations for a house with CFM50=2182 (7ach50), stack height=16 ft, floor area=2200ft2, volume=18,700ft3, flow exponent=0.65  Std 62.2 calcs from spreadsheet for whole house ventilation requirements – natural infiltration only

16  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

House Characteristics: ▪ Floor area 2200 ft 2 ▪ 16 ft stack height ▪ Leakage of 2182 cfm at 50Pa (7ach50) ▪ Volume 18,700 ft 3 ▪ Duct leakage: ▪ 12% supply ▪ 10% return 17

gfacsf1344, Seattle Washington Fan CFMACH AveHeating Load (kWh) Fan runs 8 hours per day, simulated in a house with 7 ACH50. 18

 Comprehensive measurements of infiltration in houses using a multi- tracer measurement system (MTMS)  Tracer gases injected in a controlled way to each zone. Gas concentrations were sampled every 12 minutes to measure infiltration on small time steps.  Measurement period typically lasted 2-5 days depending on the site  Data presented in report provides average values of temperature, wind speed, and measured infiltration over measurement period  Logged, interval data provides the best basis for comparison - currently have this data for one site, Site #9 19  Third in a series of reports which covered all 10 houses in the entire project.

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 House characteristics  2-story site-built house over a daylight basement  1930s era construction  Seattle  1500ft 2  20ft stack height  Electric furnace & supply ducts in basement  13ACH50  Duct leakage unmeasured  Measured data sampled every 12 minutes (5x/hr)  Model comparisons made for natural infiltration only – excluding duct leakage effects 21 March 27 Air handler on

22 April 1

 Sample SEEM simulation output showing varying infiltration and effects of duct leakage & air handler  House characteristics:  2200ft2  Seattle TMY3 climate  16 ft stack height  7ach50  Duct leakage 15% supply, 12% return 23 Air handler on April 22

 Houses with ventilation systems which operate on an hourly level can be modeled  Infiltration 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 24

 What do we mean when we say a house has 0.35ach? (effective annual average outside air changes)  “divide by 20” rule of thumb for converting BD tests to ach natural was largely derived from datasets for total infiltration in the heating season  Without mechanical sources, the natural infiltration implied by a 7ach50 test, gives effective annual ach depending on building type and climate.  To get to 0.35ach, if the blower door test is 7ach50, the annual effective air change will also include mechanical sources  New infiltration model allows (requires) us to understand (assign) separate sources of outside air: ▪ stack, wind, ducts, mechanical ventilation 25

 Infiltration calculations make SEEM more physically grounded  Leads to better understanding of house leakage and ventilation systems  Hourly schedules add more flexibility and complexity 26

 Input value calibration exercises for site-built and manufacture houses  Given existing priorities in the RTF work plan, recalibration of existing single family, site-built house simulations and measures to be conducted at a later date ▪ Potentially not until the measures sunset  Manufactured house calibrations presented later today 27

 Motion:  Adopt the updated version of SEEM, with its new infiltration calculations, for use in modeling site- built houses, manufactured houses, and small- scale multi-family buildings. 28