BUILDING SCIENCE

Heat/Energy Recovery Ventilators protocol for better IAQ in residential buildings

By Zuraimi Sultan

Researchers at NRC Construction have developed a new protocol designed to help manufacturers of Heat Recovery Ventilators and Energy Recovery Ventilators to evaluate their products more thoroughly by addressing key elements associated with indoor air quality.
Heat Recovery Ventilators (HRVs), or their moisture-transferring variants, Energy Recovery Ventilators (ERVs), are increasingly incorporated into forced air heating and cooling systems to reduce ventilation-associated heating costs in winter and cooling in summer (see Construction Innovation, December 2011). While the more common HRVs act to transfer heat from the exhausted air to the incoming outdoor air, ERVs additionally transfer moisture, therefore helping to maintain indoor humidity levels (preventing the indoor air from becoming too dry in winter and too moist in summer).
While the airflow delivery rates and heat transfer efficiency of these units can be well characterized and certified by carrying out tests specified in existing standards, the actual impact of HRVs or ERVs on residential indoor air quality is not addressed. The impact may depend on a number of factors and there was a recognized need for additional tests to address this issue.
The NRC protocol provides for an expanded evaluation of HRV and ERV systems, which includes a set of three additional tests.
One test addresses the effectiveness of particulate matter (PM) removal from the air supplied to living spaces. The protocol evaluates removal efficiencies for both 10 µm and 2.5 µm size fractions since many authorities, including Health Canada, now recognize the strong association between fine particulates (PM2.5) and cardiovascular and respiratory mortality and morbidity.
Another test reflects concern about the potential formation of by-product ozone by HRV/ERV blower motors or by supplemental electronic filtration systems that may be incorporated into the unit. The inclusion of this indoor contaminant in the protocol reflects the recent decision by Health Canada to reduce its indoor guideline level for ozone from 120 ppb to 20 ppb.
The third test addresses the emission of volatile organic compounds (VOCs) and aldehydes from the complete HRV/ERV system into the supply air. These emissions normally originate from building materials, furnishings and consumer products used indoors and can be a major source of health-related contaminants. But HRV/ERV systems and associated ductwork may also be a contributing source, as they have a significant surface area with diverse materials being in direct contact with the ventilation air. If system emissions are found to be high relative to recognized guideline levels, additional testing to determine the source is recommended; individual HRV/ERV components such as filter assemblies, casing materials, and flex duct used in installation may be tested.


Figure 1: Testing of an HRV/ERV system in a specially designed test rig


Figure 2: Air sampling for determining supply (blue) and return (red) air quality

Figure 3: Evaluating the removal efficiency of an HRV/ERV system with a particulate injection system (black box) within test rig

Testing setup
The test rig (Figures 1, 2 and 3), designed by NRC researchers for the expanded evaluation, is relatively simple in design and similar to the test platforms currently employed to evaluate the thermal efficiency of HRV/ERV units. Along with the required sampling technology, precise instrumentation for the analysis of fine and ultrafine particulates, ozone, aldehydes and VOCs is used for the expanded evaluation.
The tests prescribed in the new evaluation protocol will provide HRV/ERV manufacturers and their supply chain with a useful tool to assess and refine their products, thereby expanding market opportunities, while enabling homeowners to make informed purchasing decisions. Together, these developments are an important step toward better indoor air quality in homes.
This protocol was developed under the auspices of the Canadian government’s Clean Air Agenda, whose objective is to improve the health of Canadians through the establishment of guidelines and the creation or evaluation of technical solutions. The work was guided by a Technical Advisory Committee with members from industry associations, standards agencies, federal and provincial government departments, non-governmental organizations, and consumer associations. NRC Construction gratefully acknowledges the professional and constructive guidance provided by this Committee.

Researcher Dr. Zuraimi Sultan and technical officer Robert Magee conduct construction research at the National Research Council of Canada.

This article originally appeared in Construction Innovation Volume 17, Number 4, December 2012.