Heat Recovery Ventilator Basics And Maintenance | RasMech

Before we discuss heat recovery ventilator maintenance, we need to discuss air changes. Every facility has a certain number of air changes required for a space. Stale air must be exhaust and fresh air must be brought in. This ensures good indoor air quality and safe conditions for those in the building. A heat recovery ventilator is designed to transfer heat or coolness from this exhausted air to the intake air. In other words, HRV’s work by transferring thermal energy between exhausted air and intake air.

Heat Recovery Ventilator Function During Winter VS Summer

During the winter months the goal is to retain as much heat in a building as possible. The HRV allows the conditioned hot air being exhausted from the space to run in close proximity to the cold make-up air. This allows the warmth from the exhausted air to transfer to the cold intake air. By recovering the residual heat in the exhausted gas, the fresh air introduced into the system is preheated. This reduces the load on the HVAC system to bring the cold intake air up to comfortable temperature.

The reverse happens in the summer and the intake air is cooled by the exhaust air as it enters the building. It is important to note that there is no direct interaction between the two air supplies. The thermal transfer occurs by running the two air steams next to each other with a barrier between them. This ensures indoor air quality is not compromised.

Main Components Of A Heat Recovery Ventilator

Exhaust Duct — This duct allows exhaust air to escape the facility.

Intake Duct — This duct allows outside air into the facility

Heat Exchanger- This is where the heat transfer occurs between the air in the intake duct and exhaust duct. Heat exchanger are usually made of aluminum. They have channels to create a large surface area for the air which helps increase heat transfer.

Blower Fan- A blower fan is run by a blower motor. It is responsible for pushing air into, or out of, the facility through ducting.

Filters — These are used to ensure you aren’t bringing in contaminants with your outdoor air.

Pump — These are found in run-around heat exchangers. They are used to pump liquid between a set of two separate heat exchangers. This allows for the transfer energy between two air streams located a fair distance apart.

Heat Recovery Ventilator Maintenance Checklist

• Check blade pitch operation where applicable
• Check rotary union where applicable
• Inspect/lube blade links where applicable
• Inspect/lube spherical bearing where applicable
• Lube spider hub assembly where applicable
• Check/clean fan assembly
• Lube fan bearings
• Check belts & sheaves — adjust as applicable
• Tighten all nuts/bolts/mounting hardware
• Check motor mounts and vibration pads
• Check motor volts/amps
• Inspect and tighten all electrical connections
• Check contactors/relays, etc.
• Lube/adjust associated dampers
• Check fan operation
• Change Filters
• Lubricate pump and motor bearings per manufacturer’s recommendations
• Visually check pump alignment and coupling
• Check motor operating conditions
• Inspect electrical connections and contactors
• Inspect and clean strainers
• Check hand valves
• Inspect mechanical seal or packing as applicable
• Verify gauges if present for accuracy
• Clean external surfaces if needed

Note: Depending on the type of unit, maintenance may vary.

There are a number of different types of Heat Recovery Ventilators including:

• Rotary Thermal Wheel Units
• Fixed Plate Heat Exchangers,
• Heat Pumps
• Heat Pipes
• Run-Around
• Phase Change Materials
• Plate Heat

The Main Benefits Of HRV

Strict building codes improving efficiency have resulted in airtight spaces that suppress fresh air flow which has increased the number of HRVs in use. That is why it is so important to understand these 3 main HRV benefits:

1. It Reduces Stress On HVAC Equipment: Because of the heat transfer that occurs, it requires much less work for HVAC systems to condition the air. This means less wear and tear in equipment.

2. Improves Indoor Air Quality: By bringing in a steady stream of fresh air your indoor air quality will improve. HRV’s also run this air through filters which will reduce the likelihood of mold, mildew, fungi, dust mites and bacteria in the air. The EPA estimates that poor indoor air quality affects 33% to 50% of commercial buildings in the United States. Over 10 million work days are also lost each year from poor indoor air quality.

3. Increase Energy Efficiency : HRVs are able to transfer close to 80% of the energy between air streams.

Why HVAC System Efficiency and Maintenance Matters

HVAC systems are one of the largest energy consumers in most commercial buildings at about 25% of total energy use . Couple that with the degradation curves below, and you begin to understand that maintenance is a must.

The graph below shows a study done by the Building Owners and Managers Association (BOMA).

This study focuses on a 20-to reciprocating rooftop air conditioner with a 14-year expected life.

As you can see, the poorly maintained unit (Curve 1) resulted in a 9-year life with degrading efficiency (rising energy use and cost) throughout. The well-maintained unit on the other hand (Curve 2) achieved the manufacturers expected life of 14 years, while maintaining a high level of efficiency.

BOMA goes on to say that the failure of the well-maintained unit was caused by a compressor issue. The compressor was able to be replaced, which leads to an extension of the overall system by another 7 years.

The HRV Statistics

According to a study done by the Minnesota sustainable housing initiative :

“HRVs use electricity to power ventilation fans, on average they will save 4–5 times more energy than they consume in a cold climate. Average sensible efficiencies for HRVs are in the range of 68%-70%. High performance models can achieve sensible efficiencies in the range of 83%-84%. Average efficiency units can reduce heating energy consumption by 15%. High efficiency models can reduce heating energy consumption by up to 18%.”

Two Additional HVAC System Tips

1. Optimize Outside Airflow

Most buildings bring in more air than needed, which creates massive utility bills when heating and cooling the outside air. Reduce outside airflow rates to the minimum allowed by ASHRAE for each space. Reducing this airflow will yield significant savings!

Installing CO2 sensors in return air ductwork and maintaining interior CO2 levels will also yield some serious savings. Talk to a Temperature Control Specialist today to see if your building is running at efficient outside air temperature

2. Prevent An HVAC System Breakdown By Carrying These Parts

Below is a list of parts you can keep in stock to limit further expenses!

• Air filters
• Belts
• Capacitors
• Coil Condenser Cleaners
• Contactors
• Fuses

For larger facilities, it can be cost-effective to build your inventory of more expensive replacement parts. Especially if you have five or more pieces of equipment sharing parts like:

• Motor
• Capacitors
• Gas Valves
• Control Boards
• Compressors
• Bearings
• Shafts
• Impellers, etc.

Originally published at https://www.rasmech.com on July 12, 2021.