Simplified Space Conditioning in Low-Load Homes: Fresno, California

IBACOS anticipates that houses achieving 50% whole-house source energy savings with respect
to the Building America 2010 Benchmark (Hendron and Engebrecht 2010) will be ?low load.?
Low load is defined by IBACOS as a house with a thermal enclosure that yields a maximum
space heating and cooling load of less than 10 Btu/h per square foot of conditioned floor area
(31.5 W/m2). These small loads can be met by systems other than today?s typical ducted forced
air systems. For example, distributed fan coils with minimized ducts, terminal fan coil units, or
point source units with buoyant force or ventilation driven distribution may provide sufficient
occupant comfort in a low-load home. These systems, which can have lower total installed costs
than traditional ducted forced air systems (Stecher 2011), allow the thermal enclosure
characteristics of low-load houses to provide first-cost savings in addition to operational cost
savings.
The purpose of this study is to help determine cost-effective solutions for heating and cooling
houses that are designed to be energy efficient. This is done by testing the occupant comfort
performance of some concepts that may already exist on the market but are not in use by
production homebuilders. In some cases, the products are market available, but their use in
housing may be a new application. The standards used to assess the performance of the systems
in this study are Air Conditioning Contractors of America (ACCA) Manual RS (Rutkowski
1997) and ASHRAE Standard 55-2010 (ASHRAE 2010a).

The following systems were tested in the Fresno house:
1. Typical airflow volume ducted distribution system to the bedrooms and a single point of
delivery into the main living space
2. Low airflow volume ducted distribution system to the bedrooms and a single point of
delivery into the main living space
3. No ducted distribution to the bedrooms but over-door and bottom-of-door transfer grilles
used to facilitate free movement of air when the bedroom doors are closed and a single point
of delivery into the main living space