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It’s no secret that vivariums are “energy hogs” and that the largest source of energy consumption and carbon emissions is the use of outside air to provide high air change rates for dilution ventilation. They also have the most stringent and demanding Indoor Environmental Quality (IEQ) needs.

Traditionally, a prescriptive ventilation approach made it nearly impossible to operate vivariums efficiently. Over the last several years however, this has changed and many operators have now implemented a demand based ventilation strategy which provides both energy savings and a better environment for all occupants.

Industry Guidelines
The current ASHRAE guidance for vivarium favors performance based recommendations on air changes per hour (ACH). “Providing 10 to 15 fresh air changes per hour in animal housing rooms is an acceptable guideline to maintain macroenvironmental air quality by constant-volume systems, and may also ensure microenvironmental air quality. Although this range is effective in many animal housing settings, it does not take into account the range of possible heat loads; species, size, and number of animals involved; type of primary enclosure and bedding; frequency of cage changing; room dimensions; or efficiency of air distribution both in the macroenvironment and between the macro- and microenvironments. In some situations, using such a broad guideline might over ventilate a macroenvironment containing few animals, thereby wasting energy, or a microenvironment containing many animals, allowing heat, moisture, and under ventilated pollutants to accumulate.”

Furthermore, the current guideline speaks to sensing of the macroenvironment as a way to reduce energy costs, “VAV systems allow ventilation rates to be set in accordance with heat load and other variables. These systems offer considerable advantages in flexibility and energy conservation, but should always provide a minimum amount of air exchange, as recommended for general-use laboratories. Active sensing of contaminants in the secondary enclosure and varying the air change rates based on the room environmental conditions is one approach that can be considered to meet these requirements more energy efficiently.”

The 2011 ILAR Guide now supports a demand based approach to ventilation. In chapter 3, page 46, it states, “These systems (VAV) offer considerable advantages with respect to flexibility and energy conservation, but should always provide a minimum amount of air exchange as recommended for general use laboratories.…but variable volume systems may offer design and operational advantages, such as allowing ventilation rates to be set in accordance with heat load and other variables.”

The ILAC Council’s interpretation is to allow for an air exchange rate below the previous guideline of 10-15 ACH and to assess overall air quality and air exchange rate using performance criteria that takes into account a variety of circumstances.

Figure 1: Demand based control reduces vivarium HVAC energy by 60% vs 15 ACH. Payback is 1.4 years
Figure 1: Demand based control reduces vivarium HVAC energy by 60% vs 15 ACH. Payback is 1.4 years
Figure 2: Particle spikes are large and require increased ventilation.
Figure 2: Particle spikes are large and require increased ventilation.

Demand Based Control
With the current views, the implementation of Demand Based Control (DBC) is now possible opening vivarium facilities up to deep energy savings and first cost savings. Conventional airflow rates of 10-15 ACH are now being safely lowered down to 2-8 ACH. An ACH of 4-6 can be achieved in vivariums and 2 ACH in adjacent spaces. It is important to note that in order to achieve flows down to 2-6 ACH, all flow requirements (hoods, racks; thermal load; and ACH/dilution requirement) need to be reduced. For animal holding rooms, thermal loads are often set by the density of the animals.

A demand based control solution reduces airflow when the vivarium air is clean and increases airflow when contaminants are sensed. Nearly 98% of the time the air is clean and ventilation rates can be reduced, however if an event occurs, ventilation rates can be increased to levels of 15-20 ACH or more for purging of the environment. The variable approach is superior to fixed ACH because the flow is usually too high or low.

Varying the air change rate based on current conditions can reduce energy use by up to 50% (Figure 1). The savings can then be deployed and focused on core business and research initiatives. Retrofit projects are often combined with other deferred maintenance items to modernize the facility and operations and are significantly subsidized by utility incentives.

In a multiplexed, centralized sensing, demand based control solution, one central set of sensors is used to sense not one, but many different rooms or areas. This architecture routes packets or samples of air sequentially in a multiplexed fashion to a shared set of sensors. The sensed data is then delivered to the information management system and feedback is then given to the building management system for ventilation control purposes. The information management system also uploads the data to a data center for analysis. The solution monitors a variety of key parameters in a vivarium such as ammonia, particles, total volatile organic compounds, and other containments in the space (Figure 2).

Conclusions
Demand based control and monitoring of the IEQ of the space provides additional benefits beyond strictly energy savings. The insight produced from data collected can be used to validate safe room conditions for both people and animals. Problems with the environment that arise can be quickly investigated and diagnosed. The data can also validate efficacy and frequency of cage changing. Excess particles and allergens from poor cage practices can be detected and ammonia detection may help gauge the cage change period. Use of a central demand based control solution can also be less intrusive since sensors are remote and accurate with a freshly calibrated set of sensors installed biannually.

Developing a strategic vivarium ventilation solution such as the one described can slash vivarium energy use by up to 50% for both new and existing vivariums. This new design paradigm represents the single largest available means to cut vivarium energy use and in many cases first costs while creating a better environment for all vivarium occupants.

Dan Diehl has over 25 years of industry expertise across a wide variety of vertical markets and disciplines in commercial and light industrial building markets. Dan has been an integral part of the growth and success of Aircuity, leading global sales for his first four years with the company before being appointed CEO. Previously, he led business development at Lutron Electronics, an industry leader in lighting controls. Prior to Lutron, Dan was a partner for six years with Synergy, an energy services company that delivers energy efficiency programs for national clients in the light industrial sector. Dan began his career with Johnson Controls, Inc. working for 11 years with increasing responsibilities in sales, branch, and regional management positions.

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