Energy Recovery Ventilators Explained

ERV - Aldes Canada

Energy Recovery is one of the major ways to reduce the energy consumption of a building without replacing major equipment or using renewables. The global environmental burden from carbon from the impact of buildings is on the order of 30-40% and is a huge opportunity to introduce efficiencies. Energy recovery is the concept of utilizing a waste stream of energy within a process to reduce or eliminate a different fuel-consuming process. This concept is useful in complex systems such as an industrial refrigeration plant or in cases as simple as a single residential dwelling. Energy Recovery Ventilators within Building HVAC systems are a simple technology under-utilized in Alberta. In each climate, building HVAC is a completely different puzzle. Focusing on Alberta, we have a dry climate and a very large range of temperatures experienced within the year and even day, with a heavy majority of cold conditions. Energy recovery ventilators (ERV's) take exhaust air from buildings and use it to pre-heat outdoor air or fresh air intake for ventilation needs. The simple process is shown below: 

 

In a residential case, a small ERV unit would take exhaust air from the kitchen and washroom spaces that are at room temperature and use it to heat up fresh air for ventilation. Warm stale air has a lot of usable energy when outdoor temperatures can be as low as -40 deg C. This would essentially recycle the warm air inside the building, which would take a huge load of the primary heating system and reduce the need to open windows for fresh air. In commercial applications, there can be substantial energy savings benefits and paybacks depending on facility use if there is a lot of exhaust air. Highly occupied areas that have high ventilation needs, kitchens with many exhaust hoods, labs, institutions, garages and workshops with fume hoods or processes requiring exhaust air are all excellent candidates. In larger applications, there is a variety of technology that can be adjusted for individual building needs and constraints, such as enthalpy wheels or heat exchangers of varying materials and properties. These ventilators can be assisted by electric or wet pre-heat coils for extreme conditions and feed and mix with re-circulated air in larger and more complex air handling systems. ERV's can also be utilized as mechanisms of free cooling in shoulder seasons by simply bringing in fresh outdoor air to provide cooling in any type of space.

 

Other than energy recovery, these systems also enhance the indoor air quality in buildings. North Americans spend 90% of their time indoors (on average). Often a mix of mechanical and natural ventilation is used; natural ventilation is more common in residential spaces through windows and infiltration. Therefore, proper ventilation can often depend on drafty, inefficient building envelopes. The current minimum standard for mechanical ventilation on new buildings is governed by ASHRAE 62.2 (residential) and ASHRAE 62.1 (commercial). To meet ventilation without any heat recovery takes considerable natural gas for burners to heat air at a temperature differential of up to 60 deg C. An ERV system ensures fresh air delivery into existing spaces that may or may not comply with ASHRAE, on regular intervals, or on a demand-based depending on control systems. Air Filters are also used on these units, which will purify the air intake, which is a growing concern with increasingly bad cases of air quality during smoky summer months. Heat Recovery Ventilation upgrades can provide opportunities for commercial buildings to not only increase efficiency and decrease operational costs but also increase occupant productivity. Indoor Environment Quality of a workspace consists of factors like air quality, thermal comfort, lighting levels, controls accessibility and daylight exposure which directly correlates to occupant health, comfort and performance. Personnel costs for businesses or retaining residential tenants are high costs and risks. Upgrading a ventilation system is a major step towards social and fiscal responsibility.

 

The British Columbia Building Code already mandates the use of ERV's even in residential applications. Alberta is behind for a variety of reasons - natural gas, as well as electricity, has been reasonably cheap for a long time, and building owners have not prioritized reductions based on financials alone, even if there is a reasonable payback. Often developers designing and constructing buildings will never operate the buildings and therefore minimize construction costs and meet only the minimum requirements of codes and permits. With a slow economy and tighter budgets, some of the first things to go into building projects are "fancy controls", high-efficiency equipment, and systems that you can't see. With advancements towards carbon reduction goals on all levels of government and well as a push from personal and corporate social sustainability goals, it is a matter of time until efficiency measures in buildings are mandated for all. Why not now?

 

We are experts in HVAC and Mechanical systems design as well as energy auditing, tracking and carbon offsetting. Ask us about your next project!

 

 

About Aldes