When it comes to Energy Recovery Ventilators (ERVs), a fully dedicated installation stands out as the pinnacle of flexibility and efficiency, but what does full dedication mean and why is it desirable? This discussion will be limited to residential style ERVs – which can be installed in single family homes and are most commonly found in each unit of a multifamily residential project. They deal with airflows in the range of 50-150CFM, exact values are determined from section 403.4.2 of the International Mechanical Code (IMC).
The namesake dedication refers to the style of the ductwork transmitting ventilation air between the ERV casing and the occupied space. This makes it primarily a topic of installation, but some coordination with equipment design and selection will of course also be necessary. A dedicated ERV is one that does not depend on the ductwork or fans of any other equipment to deliver or exhaust ventilation air. Partially dedicated or simplified systems, on the other hand, tie the ventilator supply or supply/exhaust into the return ductwork of the forced air heater / AC unit. This allows for less ductwork and an easier retrofit process, but as we’ll see below a fully dedicated system has several advantages.
Key Characteristics of a Fully Dedicated System:
1. Meeting Specific Exhaust Needs: Fully dedicated ERV installations offer the ability to exhaust air directly at the source of unwanted contributions to indoor air – in kitchens and bathrooms. This design allows exhaust air to be incorporated into the energy recovery core with ease.
2. Simplicity of Equipment Install: When an ERV is tied into the ductwork of a forced air heater/AC unit, that fan must run continuously or the ERV and forced air system must be interlocked. A fully dedicated ERV avoids these coordination headaches.
Let’s take a moment to introduce what can be considered the next step above a fully dedicated ERV system, a distributed system. A distributed ventilation ductwork system is outlined in the IMC as one that delivers ventilation air directly to all spaces of a dwelling unit. When ductwork systems are distributed, less total ventilation air is required to be brought into the conditioned space because that ventilation air is going to be delivered more thoroughly to the breathing zone of the occupants. With that in mind, let’s continue exploring the benefits of these distribution strategies.
1. Code Compliance: Code requirements will vary depending on your location, building type, etc. Ventilation air may be required to be delivered directly to occupied spaces, downstream of heating or cooling coils, and further, the aforementioned distributed system ventilation rate reduction could incentivize a distributed ductwork design which would also require that the system be fully dedicated. Refer to design by a registered professional or local authority having jurisdiction to find out what code provisions apply to your installation.
2. Reduced Energy Consumption: A fully dedicated system will save energy consumption and operating cost in multiple ways. If the ERV and forced air system are interlocked as in a non-fully dedicated system an extra fan will be operating when heating and cooling are not called for. The extra run time for that fan will use energy that a fully dedicated system will not. In a multifamily application the reduced ventilation rate from a distributed system will translate to lower fan energy use and consequent savings.
3. Flexibility in Duct Installation: The final volume of delivered fresh air in a residential ventilator is dependent on the external static pressure in the ductwork. The higher the static pressure in the duct system, the less airflow can be expected from the unit fans. In a multifamily application the reduced ventilation rate from a distributed system will allow a higher external static pressure in the ductwork. This will aid the installer by allowing greater flexibility in the details of the ductwork installation.
The fully dedicated ERV installation stands as a testament to flexibility, efficiency, and code compliance in modern ventilation strategies. From precision air distribution to reduced operating costs, this approach offers a holistic solution for enhanced indoor air quality.