Green Building Library
Space Heating and Cooling
HVAC Energy Cost Savings Rules of Thumb
Although architects are not expected to design HVAC systems, they must be able to understand basic concepts when planning their buildings. In many cases one must know the kinds of questions to ask of the mechanical designer. The following rules of thumb can serve as points of discussion to ensure the mechanical designer is doing the utmost towards energy efficient design.
Building Enclosure
Use building insulation to minimum ASHRAE 90.1 standards.
Glazing
If daylighting design is not contemplated, reduce cooling loads with low shading coefficient glazing. To avoid compromising the view or quality of natural light, maximize K-value.
Electrical
Any reduction in electrical loads will have corresponding cooling load reductions.
Infiltration
Infiltration rates of 1/2 to 1/3 air changes per hour in office buildings are a good design standard for mechanical systems. Ensure that air tightness meets this parameter.
Ventilation
Use the lowest possible ventilation rate that still allows a healthy working environment. The advent of nonsmoking buildings may allow lower ventilation rates.
Economizer Cycle
Investigate the addition of an economizer cycle to the ventilation system to reduce energy for cooling. When ambient conditions permit, outside air is used in lieu of the cooling plant. Ensure that continuing maintenance prevents controller drift and damper leakage above 3% or any savings will be diminished.
Extended Deadband Setpoints
Consider a wider deadband on the heating and cooling setpoints. The traditional 2°F (1°C) range from 72° - 74°F (22° - 23°C) can sometimes be extended to 70°F (21°C) for heating setpoint and 78°F (25°C) for cooling setpoint.
High Efficiency Boilers (>85%)
Consider substituting High Efficiency Boilers (Gas Fueled) for conventional boilers. Sizes are currently available up to 150,000 Btu/H. These are workable in temperate or cold climates for medium-sized office buildings with requirements for backups.
Increased Coefficient of Performance (COP)
ASHRAE 90.1 specifies minimum COP for most equipment. In many cases for a nominal first capital cost. Increased COP can result in substantial energy savings because of their increased efficiency.
System Compartmentalization
If HVAC systems are designed to accommodate smaller zones, then meeting thermal and ventilation requirements on a highly local basis eliminates associated energy-costly zone control (i.e., reheat) and ventilation and transport inefficiencies normally associated with centralized HVAC systems. An added benefit is greater individual zone control and flexibility for different users.
Excerpted with permission from Design Smart published by BC Hydro.
