BA-0413a: The Snapshot—A Quick Description

The Snapshot: A Quick Description

SNAPSHOT stands for Short, Non-destructive Approach to Provide Significant House Operation Thresholds. It is the test form that we use in the Building America program to ascertain house performance and specifications.

This technique incorporates the field characterization of critical parameters, (thresholds of operation) for indoor environment, thermal comfort, air delivery and distribution systems as well as their interaction with the building envelope. The data collected will then be used as direct inputs to energy prediction tools, such as REM/Design or DOE-2. The major parts of the testing include building envelope leakage (aka blower door test), duct leakage test (Duct Blaster®), and differential pressurization of zones. Also, the form provides a place to collect information on mechanical equipment and ventilation systems.

Using the Snapshot Form (Instructions and Hints)

The Snapshot is done in order to have an effective and concise record of house performance and specifications for the Building America program.

The top includes information on the location (lot #, address, subdivision), model type, and date & time.

Initialization

• Square feet (as measured by real estate numbers)
• Surface area: this is used to obtain our envelope infiltration goal (2.5 square inches of leakage area per 100 sf of envelope); it includes the foundation, such as slab and/or basement walls.
• Volume: volume of house in cubic feet; provides air change information
• Windspeed: estimated (5, 10, 15 mph); tests in high wind conditions are often suspect
• Outside temperature: to provide order of magnitude of stack effects; also used in TECTite
• Check all registers and bedroom doors (equalize into one zone)
• Measure static pressure in return between fan & filter (used for supply-only AirCycler™ systems)
• Static pressure in Supply and Return (estimates airflow through AHU; useful as an indication of restrictive duct systems. Measure across AHU cabinet, not including add-on coils or pleated media filters, if possible).
• Is there a ventilation system (yes/no)
• Type of ventilation system (e.g., exhaust-only, HRV or ERV, AirCycler™ supply-only system)
• If there is an AirCycler™, enter the off / on times (in minutes)
• Enter outside air duct pressure (carefully make hole for pressure probe through duct wall; see Addendum II for a table relating duct pressure to airflow)
• Type of outside air duct (type—flex/sheet metal, and diameter)
• Is there an adjustable outside air damper (yes/no)
• Is there a fireplace or wood stove (yes/no)
• Duct location (approximate fraction in attic, conditioned space, basement, etc.) 

Pressure Testing

• The next group of tests can be run at the front door, measuring house main space pressure with respect to (WRT) outside. You should be able to read it off one of the pressure taps that you have set up already to perform the blower door test.
• Stack Pressure (take a baseline measurement with blower door installed; covers on)
• Dominant Duct Leak Effect (baseline with HVAC system running)
• Master Bedroom Door Closure Effect (with HVAC running, what is main space WRT outside when master bedroom door is closed; i.e., shuts off some of the supply flow to the main space)
• All Doors Closed Effect (with HVAC running, what is main space WRT outside when all doors are closed)
• Fireplace/Wood Stove Zone HVAC Test (what is the worst negative pressurization WRT outside in the zone that contains the fireplace or wood stove? Turn on exhaust fans, dryer, and open and close doors for worst case. Should not be greater than 5 Pa.)
• Pressure In Each Closed Room (what is the pressure in a bedroom WRT the main space when the door is closed? Often a problem due to lack of transfer grilles or returns; room becomes pressurized, increasing infiltration, and decreasing supply flow). 3 Pa is used as the Building America threshold.

Blower Door Testing (BDT)

• Blower Door Location (front door, garage door, etc)
• Total CFM 50 (cubic feet per minute at 50 Pa)
• Add C & n values if available on multipoint test: provided in results of TECTite computerized blower door test; adds further information about leakage characteristics, and is statistically better data due to multipoint testing.
• If there is a conditioned space that is typically sealed from the main space (i.e., sealed conditioned attic, sealed conditioned crawl space, conditioned kneewall sections), please run the test with the access to that space open. It provides information on how well sealed the total conditioned space is. This is the number that should be reported for pass/fail criteria.

Duct Airtightenss Testing (DAT)

CFM 25 total: if a first submission to BSC, provide information on how ducts were sealed (to inside of boot, at face of register, etc), type of test (pressurize or depressurize), and location of pressure tap.

CFM 25 outside (requires both blower door and duct blaster setup; leak to the outside is more significant than total system leakage for energy calculations).

Mechanicals

• Furnace or air handler (if heat pump or fan coil unit) (Make and model)
• Air Conditioner (Make and model of outdoor unit); include indoor coil model, if an add-on part on air handler.
• Domestic hot water (Make and model)
• If there are multiple units, please use the back of the form, or customize an electronic copy to your own specifications.
• If there is other equipment of interest (HRV/ERV, humidifiers, electrostatic filters) please note that here as well. . .

Download the Snapshot Instructions here. Download the Snapshot Form here.