Guidebook for Energy Efficiency in Municipalities

Energy efficiency and the building envelope
T2
Apart from reducing energy consumption, the benefits of an energy-efficient building
envelope include:
lower cost of air-conditioning plant, as smaller quantities of heating and cooling are
required at peak periods (often, the capital savings on HVAC plant can almost pay for
the extra cost of insulation and other energy-efficient features—before the value of
ongoing energy savings is even considered);
lower charges for peak energy demand;
improved occupant comfort.
The energy efficiency of an existing building envelope can be improved by a variety of
measures. While this may not save on investment in heating and cooling plant, it can still
cut peak energy demand charges, reduce operating costs and improve occupant comfort.
For example, where air-conditioning equipment is being converted to eliminate the use of
CFCs, the replacement refrigerants may have different properties, and this may reduce
the cooling capacity of the plant. Rather than investing in extra equipment to compensate
this, upgrading the energy efficiency of the building envelope is a good alternative, as this
option also reduces peak capacity requirements and cuts ongoing energy costs as well.
Constraints to overcome
Efforts to improve the thermal performance of a building are often treated as a low priority
for a number of reasons:
Building design is the responsibility of the architect, while engineers look after HVAC
design (including calculation of heating and cooling loads, which provides valuable
information about which elements of the building envelope contribute most to heating
and cooling energy consumption and peak demand). Often communication between
the two is poor. Appropriate contractual arrangements and/or use of a project
manager or coordinator can overcome this.
HVAC designers are often paid a percentage of the cost of the HVAC system, so they
have no incentive to help the architect reduce HVAC size and cost.
Many designers believe that an energy-efficient building envelope may increase
energy consumption by trapping heat generated by lights, equipment, and people
inside the building.
Energy efficient building design is perceived to be expensive, but the appropriate
orientation, sizing, and selection of glazing can actually reduce envelope costs.
Opportunities for savings
Savings on HVAC operating costs (and greenhouse emissions) through energy-efficient
building design can range from 20 to 50%.
Glazing
Up to a kilowatt of heat can enter a building through a square metre of clear glass
exposed to direct sun, which is equivalent to switching on a single-bar electric heater at
the hottest time of the day. Winter heat loss through each square metre of single glazing
is three times that through uninsulated wall, and more than 10 times the loss through a
square metre of insulated wall. This adds to peak electricity demand (often incurring extra
demand charges), requires increased HVAC system capacity, and creates glare and
occupant discomfort.