Improving air quality and energy efficiency: a winning combination in industry

In industrial buildings, good indoor air quality (IAQ) is critical to the health and safety of workers. In these facilities, contaminant emission rates can be ten to one hundred times higher than in non-industrial facilities. In order to ensure adequate air quality, there must be adequate fresh air ventilation to reduce or eliminate the presence of contaminants, toxic products from processes and other products that are harmful to our health. In this article, we will look at different ways to ensure efficient fresh air supply.

In Quebec, the Regulation respecting occupational health and safety stipulates minimum ACPH rates for specific establishments. Here are some examples:¹

Classification of establishments	Minimum ACPH rate
Glass and glass products manufacturing	4
Metal fabricating industries	4
Cement industry	3
Slaughterhouses and drysalting	2
Tire and tube manufacturing	3

In addition to the emphasis on air quality, it’s important to create a slightly positive indoor air pressure to prevent a variety of issues—a design element that’s often overlooked by plant managers. When the air pressure inside a plant is negative compared to the outdoor pressure, this deficit causes an issue with extinguishing burners, which impacts the efficiency of all combustion devices used inside the building envelope (including processing equipment). This can lead to unplanned interruptions, significant production losses, and unnecessary costs.

The right equipment makes a difference

In order to comply with regulatory standards for indoor air quality and ensure proper combustion within an industrial building, high-flow ventilation equipment is required. Standard equipment in this context uses vast amounts of energy, particularly in facilities requiring a high ACPH rate, such as very large plants. When you need fresh air intake for ventilation purposes, using a direct-fired makeup air unit is a good basic solution for the makeup air. As shown in figure 1a below, the combustion air is drawn from the fresh air intake via an air burner (see figure 1b), and the combustion products are fed directly into the heated air. For this reason, this device is better suited to certain commercial and industrial applications than to residential or commercial applications.

In addition to providing very high air efficiency (95% or more), this type of unit makes it easy to heat large volumes of air to compensate for the negative pressure issue often present in plants. Because this equipment is considered a basic solution, it should be used in combination with other industrial ventilation units that recover energy to further reduce the energy used for heating.

Characteristics of efficient ventilation equipment

To ensure efficient air changes and maintain a slightly positive pressure, stale air must be removed and replaced with fresh air. However, exhausting this air without recovering the energy within it wastes money and energy, and generates significant GHG emissions.

A good option is an air-to-air heat exchanger that:

transfers heat between air streams to optimize energy recovery;
allows partial transfer of humidity via the pressure differential between the two air streams; and
minimizes the transfer of air, other gases (e.g. pollutants), biological contaminants, and particulate matter between the air streams and the fresh air.

Examples of efficient ventilation technologies

There are several efficient ventilation systems, each with its own advantages and disadvantages. See table 2 below for more information on their characteristics. Now let’s take a closer look at the thermal wheel and the coil system.

Table 2

This table summarizes the characteristics of the different heat recovery technologies.

Type of system	Efficiency (%)	Latent heat recovery	Air separator
Plate	70-80	Yes	No
Thermal wheel	70-85	Yes	No
Coil (run around)	45-65	No	Yes
Heat pipe exchanger	60-75	No	No
Cassette exchanger	60-80	Yes	No

The thermal wheel

Installing a thermal wheel may be a good way to increase the energy efficiency of a ventilation and air exchange system.

It is a cylindrical air-to-air heat exchanger (wheel) made of aluminum sheet metal, which constantly rotates. Half of the wheel surface is in contact with the exhaust air and the other half with the intake air to be heated, as shown in figure 2a. A thermal wheel not only transfers heat, it also transfers humidity through an applied coating, such as silicate gel.

With an efficiency of 85%, this technology can be quite large, with a wheel diameter that can exceed 3 m (10 ft.). Engineers and contractors must ensure that the roof structure is able to support this additional weight. This type of equipment can be used for extremely high-flow ventilation needs, so it is ideal for very large industrial spaces. Finally, thermal wheels are self-cleaning, thanks to the alternating airflow generated by each rotation of the wheel. Figures 2b and 2c show a thermal wheel designed by Navada and manufactured by Concept Air for a plant in Quebec.

The coil or run around

A run-around energy recovery loop consists of coils positioned within the supply and exhaust air streams of a ventilation system. The coils are looped via pipework that is charged with heat transfer fluid, often a glycol-based antifreeze.

Run-around energy recovery loops are extremely versatile and particularly suitable for industrial applications, as the supply and exhaust loops are fully separated. This allows for optimal placement of extraction fans where a significant amount of heat is available for recovery (e.g. process areas, furnaces). This system also requires very little maintenance because the only moving parts are the pump and the valves. However, to ensure its optimal operation, the air must be filtered, the coil surface regularly cleaned, the pump and valves maintained, and the transfer fluid refilled or replaced periodically.

It is important to note that this heat recovery technology can only recover thermal energy. It cannot capture the humidity between air streams due to the distance between flows. With equal and non-condensing airflows, typical performance values for a coil system range from 45% to 65%.

Conclusion

For a ventilation system to achieve a high level of efficiency in an industrial setting, particularly in heavy industry, a heat recovery strategy is essential.
For Quebec businesses, this type of strategy has several advantages, not least of which is protection against energy price volatility and a concrete reduction in GHG emissions. Furthermore, Énergir’s grants can help make these projects more cost-effective and economically attractive.
If you would like to discuss the best solutions for your needs and the Énergir grants available for your ventilation projects, please get in touch with our DATECH experts.

GRANTS AVAILABLE THROUGH ÉNERGIR

Énergir offers several grants to encourage its customers to achieve high levels of efficiency in plant ventilation. Grants for adopting these systems and the necessary equipment are available under Énergir’s Studies and Implementation programs.

1. The Feasibility Study grant aims to help companies do feasibility studies with a consulting engineering firm to evaluate different scenarios to reduce energy consumption. It will cover a portion of the cost of a feasibility study on energy efficiency measures, to be conducted by a consulting engineering firm registered with Énergir. The grant available to customers is:
The lesser of the following amounts:

50% of the cost of the study, before taxes; or
$50,000 per account number, per fiscal year.

2. The Implementation grant helps to implement energy efficiency measures identified in the feasibility studies. The two examples discussed in the article (thermal wheel and cassette ventilation unit) are eligible initiatives under these programs. The maximum annual grant amount cannot be more than $1 million, or 50% of eligible project costs before taxes (estimated project additional costs), including equipment, installation and engineering costs. Under this program stream, the grant is awarded based on the business line and on the return on investment calculated by energy efficiency measure, before grants.