4.5   Controls    

4.5.1    Thermostats    

Automatic setback thermostats can add both comfort and convenience to a home. Occupants can wake up to a warm house in the winter and come home to a cool house in the summer without using unnecessary energy.

A thermostat is always required for central systems whether the prescriptive or performance compliance method is used. An exception is allowed only if:

1.   the building complies using a computer performance approach with a non-setback thermostat; and

2.   the system is one of the following non-central types:

a.   Non-central electric heaters

b.   Room air conditioners

c.   Room air conditioner heat pumps

d.   Gravity gas wall heaters

e.   Gravity floor heaters

f.    Gravity room heaters

g.   Wood stoves

h.   Fireplace or decorative gas appliances

When it is required, the setback thermostat must have a clock or other mechanism that allows the building occupant to schedule the heating and/or cooling set points for at least four periods over 24 hours.

If more than one piece of heating equipment is installed in a residence or dwelling unit, the set-back requirement may be met by controlling all heating units by one thermostat or by controlling each unit with a separate thermostat. Separate heating units may be provided with a separate on/off control capable of overriding the thermostat.

Note that thermostats for heat pumps must be “smart thermostats” that minimize the use of supplementary electric resistance heating during startup and recovery from setback, as discussed earlier in the heating equipment section.

4.5.2    Zonal Control    

An energy compliance credit is provided for zoned heating systems, which save energy by providing selective conditioning for only the occupied areas of a house. A house having at least two zones (living and sleeping) may qualify for this compliance credit. The equipment may consist of one heating system for the living areas and another system for sleeping areas or a single system with zoning capabilities, set to turn off the sleeping areas in the daytime and the living area unit at night (see Figure 4-20).

There are unique eligibility and installation requirements for zonal control to qualify under the Standards. The following steps must be taken for the building to show compliance with the Standards under this exceptional method:

1.   Temperature Sensors. Each thermal zone, including a living zone and a sleeping zone, must have individual air temperature sensors that provide accurate temperature readings of the typical condition in that zone.

2.   Habitable Rooms. For systems using central forced air or hydronic heating each habitable room in each zone must have a source of space heating such as forced air supply registers, radiant tubing or a radiator.  For systems using a combination of a central system and  a gas vented fireplace or other individual conditioning units, the zone served by the individual conditioning unit can be limited to a single room. Bathrooms, laundry, halls and/or dressing rooms are not habitable rooms.

3.   Non-closeable Openings. The total non-closeable opening area (W) between adjacent living and sleeping thermal zones (i.e., halls, stairwells, and other openings) must be less than or equal to 40 ft². All remaining zonal boundary areas must be separated by permanent floor-to-ceiling walls and/or fully solid, operable doors capable of restricting free air movement when in the closed position.

Figure 4-20 – Zonal Control Example
Source: Richard Heath & Associates/Pacific Gas & Electric

4.   Thermostats. Each zone must be controlled by a central automatic dual setback thermostat that can control the conditioning equipment and maintain preset temperatures for varying time periods in each zone independent of the other.  Thermostats controlling vented gas fireplace heaters that are not permanently mounted to a wall are acceptable as long as they have the dual setback capabilities.

Other requirements specific to forced air ducted systems include the following:

1.   Each zone must be served by a return air register located entirely within the zone. Return air dampers are not required.

2.   Supply air dampers must be manufactured and installed so that when they are closed, there is no measurable airflow at the registers.

3.   The system must be designed to operate within the equipment manufacturer's specifications.

4.   Air is to positively flow into, through, and out of a zone only when the zone is being conditioned. No measurable amount of supply air is to be discharged into unconditioned or unoccupied space in order to maintain proper airflow in the system.

Although multiple thermally distinct living and/or sleeping zones may exist in a residence, the correct way to model zonal control for credit requires only two zones: one living zone and one sleeping zone. All separate living zone components must be modeled as one single living zone; the same must be done for sleeping zones.