Performance Areas of Current Concern

Building Envelope

The building envelope is important to the performance of a house, because the envelope thermal loads dominate the house heat transfer mechanisms. This is different from commercial buildings, where the internal loads dominate. Assumed thermal loads, equipment sizing, structural durability, and occupant comfort for houses are based on having the building envelope perform as intended, including windows, airtightness, and insulation levels. In new houses, installation failures, especially in insulation and air sealing, can cause problems. In existing houses, subsequent loss of durability can also decrease performance. Poor material selection, handling, and installation (e.g. insulation settling, air barrier damage from UV exposure) can result in performance reductions over time.

Cooling Equipment and Heat Pumps

Even in new houses, cooling systems rarely perform as intended. Refrigerant charge level, airflows across coils, and other operating conditions often do not meet manufacturer’s or system design specifications. As a result, these problems often degrade the capacity and efficiency of the cooling equipment.

Heat pumps share many of the same problems associated with cooling systems, but have some unique features. Use of electric resistance ("strip") heaters can significantly increase energy consumption. To perform well, heat pump (and desuperheater based) water heaters require careful integration with the building.

Air Distribution Systems

Ducts that are part of the thermal distribution system may be the single worst performer in the energy performance of a house. Duct leakage, duct insulation compression, and other poor installation practices can reduce duct efficiency by 30% from even a moderate level of design performance.

Compared to the space conditioning system, the ventilation system in most houses is simple. It usually consists of operable windows, infiltration, and a few (if any) intermittently-operated local exhaust fans. However, some houses also use whole-house ventilation, which sometimes is integrated with the space conditioning system.

The delivery effectiveness and room by room distribution efficiency of both the thermal and ventilation distribution systems depends on the proper flow of air through the air moving equipment. Poor operation of the air distribution systems can cause comfort problems, structural moisture problems, and poor indoor environmental quality, as well as wasted energy.

Combustion Appliances

In addition to fuel-related issues for these kinds of appliances, poor operation of vented and non-vented appliances can reduce their efficiency and indirectly affect electricity usage. Fueled appliances must vent as intended. Poor installation of either the combustion equipment or air moving equipment can reduce efficiency. In some cases, it can also lead to backdrafting, combustion gas spillage, or other hazards such as heat exchanger corrosion. Such events, along with insufficient ventilation for unvented combustion appliances, can directly affect the indoor environment by causing health, comfort, or indoor air quality problems.

Indoor Air Quality

Related to the performance of thermal and ventilation distribution systems is a host of indoor air quality issues that apart from the airflows themselves include the generation, transport, and removal of pollutants. Examples of pollutants in houses include gaseous ones such as carbon monoxide, nitrogen oxides, volatile organic chemicals, and radon; biological ones such as molds, fungi, and mites; and particulates such as soot and dust.

Controls

In commercial commissioning, control problems are the key item of concern. While not as important in houses, controls can still play an important role, especially when the systems become complex (e.g. multistage systems, integrated heat-pump/ventilation systems). Even common heating setback / cooling setup thermostats need to be properly commissioned. Making sure that these controls are doing what was intended or is appropriate is often crucial to achieving good energy performance.

Other Appliances

Apart from the HVAC system, there are many other appliances in a house. Some of them (e.g. water heaters, stoves, refrigerators, clothes dryers) can consume large amounts of energy. Improper configuration of some appliances (e.g. a clogged dryer vent) can also cause poor performance. Most of these appliances require only simple commissioning.