Heat Recovery Ventilator for Commercial Applications
Commercial Ventilation: Heat Recovery vs. No Heat Recovery
A heat exchanger to heat or cool incoming fresh or outside air, capturing about 50% to 70% of the sensible heat from the exhaust air that would otherwise be discharged into the atmosphere.
Item ID: 20
Technical Advisory Group: 2010 HVAC TAG (#3)
Average TAG Rating: 3 out of 5
TAG Ranking Date: 06/29/2010
Technical Advisory Group: 2015-1 Commercial HVAC TAG (#11)
Average TAG Rating: 3.1 out of 5
TAG Ranking Date: 03/10/2015
TAG Rating Commentary:
- When combined with a ductless heating and cooling distribution system this is a huge energy savings. The savings must be understood in relation to what it allows from the other system. When you pull the ventilation air out to an ERV, then you can use a ductless heating and cooling system (such as VRF) and cycle the heating and cooling fans off unless there is a call for heating or cooling. Then not only are we capturing the heat recovery energy, but dramatically impacting the fan energy of the system.
- This is required by code in several applications, and if the heat is gas, the savings will be gas.
- Would most likely be gas savings
- Many products are already on the market, from various OEMs. AHRI is now working on a way to rate the combination of an ERV with a packaged AC (RTU). MT program justified, but is it an ET research area?
- Good with automated controls for monitoring
- Very good saving for many climate zones - less for mild climates where outside air can be used.
- Very tough to find applications where this technology is cost-effective.
When outside ventilation air is introduced into the interior of a building at a higher or lower temperature than the building temperature, it must be heated or cooled (Roth 2010). Heat recovery ventilation (HRV) systems provide a controlled way of ventilating a building while minimizing energy loss. This technology reduces the costs of heating ventilation air in the winter by transferring sensible heat from the warm inside air being exhausted to the incoming fresh (but cold) outside air. The fresh outside air is not mixed with the stale indoor air that is being exhausted. In the summer, the inside air cools the warmer supply air to reduce cooling costs and can assist in removing moisture from the outside air.
HRVs with flat plate counterflow heat exchangers or heat pipes capture about 50% to 70% of the heat from the exhaust air that would otherwise be lost to the outside with traditional HVAC designs. This pre-heating or pre-cooling results in a 30% reduction of total heating and cooling loads. HRVs can be used for small commercial applications, education/classrooms, nursery school facilities, hospitality applications, and in healthcare and retirement communities. They are also supplied for air-tight residential or multifamily units.
Baseline Description: Untreated Outside Air for Ventilation
Baseline Energy Use: 10.5 kWh per year per square foot
The 2009 Commercial Building Stock Assessment gives the actual electrical building energy use index (EUI) for various types of heating and cooling systems (Table D-EA5). Office buildings with electric heating and cooling have an EUI of 20.1 kWh/sf/year. Office buildings with no electric heating or cooling use only 8.2 kWh/sf/year, indicating that the combined HVAC heating and cooling energy use is 11.9 kWh/sf/year. (For all commercial buildings, the corresponding values are 19.9 and 9.4 kWh/sf/year, respectively, for a combined heating and cooling electrical energy use of 10.5 kWh/sf/year).
Because this technology can be applied to many types of non-office buildings, a baseline energy use of 10.5 kWh/sf/year is assumed (NEEA, 2009).
Manufacturer's Energy Savings Claims:
"Typical" Savings: 30%
Savings Range: From 10% to 50%
A heat recovery unit will save about 70% of the cost to heat, cool, and precondition outside air at a specific condition, as determined by AHRI (Standard 1060-2000). Because outside air conditions vary greatly across the U.S., the actual savings will vary depending on location.
Best Estimate of Energy Savings:
"Typical" Savings: 30%
Low and High Energy Savings: 15% to 70%
Energy Savings Reliability: 5 - Comprehensive Analysis
Most HRV systems can recover about 50% of the heat in the exhausted air and transfer that energy to the incoming air. They are most cost effective in climates with extreme winters or summers, and where fuel costs are high. Modeling HRVs for the Pacific Northwest climate indicates an overall HVAC energy savings of about 30%.
The energy savings depend on the volume of outside air that is required to be delivered to the building or space and the climate conditions. Proper design, equipment selection, and commissioning are also crucial for realizing energy savings.
Energy Use of Emerging Technology:
7.4 kWh per square foot per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
This technology could be used for virtually any commercial building, but BPA considers only those that are electrically heated. The entire commercial building stock in the Northwest that has conditioned space that is electrically heated is calculated to be 84.7% x 27.1% (Table C-GB13). The total commercial floor space that would benefit from the retrofit of this technology is estimated at 2,640,946,000 x 27.1% = 715,969,366 sf.
Regional Technical Potential:
| || Total Commercial Floor space || % Conditioned || Conditioned space |
| Source, units || (NEEA, 2014) (sf) || (NEEA, 2009, App C ) || (sf) |
| || 3,118,000,000 || 84.7% || 2,640,946,000 |
2.26 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: square foot
Emerging Technology Unit Cost (Equipment Only): $1.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.00
Baseline Technology Unit Cost (Equipment Only): $0.00
The cost of implementing HRV can vary greatly depending on the specific system design and exhaust system layout. A 400 cubic foot per minute (cfm) unit will cost about $1,500. A 2,000 cfm unit will cost about $2,500. The incremental cost, dollars per cfm, of outside/exhaust air will decrease as the outside/exhaust air volume increases.
Simple payback, new construction (years): 3.5
Simple payback, retrofit (years): 3.5
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
The cost of implementing HRV can vary greatly depending on the specific system design and exhaust system layout. In general, simplicity is the key to a cost-effective installation. To save on installation costs, many systems share existing ductwork. Complex systems are not only more expensive to install, but they are generally more maintenance intensive and often consume more electric power. Payback periods in the Northwest tend to be long, especially in mild climates west of the Cascade Mountains.
A heat recovery ventilator (HRV) can help make mechanical ventilation more cost effective by reclaiming heat from exhaust airflows. HRVs use heat exchangers to heat or cool incoming fresh air, recapturing about 70% of the sensible heat from the exhaust air that would otherwise be lost to the outside with traditional ventilating units. HRV systems provide a controlled way of ventilating a building while minimizing energy loss. They reduce the costs of heating ventilated air in the winter by transferring heat from the warm inside air that is being exhausted to the fresh (but cold) supply air. In the summer, the inside air cools the warmer outdoor air to reduce ventilation cooling costs. The best HRV has a bypass for the economizer cycle, which typically operates at ambient temperatures between 55°F and 65°F.
A similar and competing product, called the energy recovery ventilator (ERV), transfers or recovers both sensible and latent energy using a rotary heat wheel. In commercial applications in humid climate zones in the U.S., an ERV can help deliver the greatest energy savings benefit and also greatly improve humidity control (Hoger, 2009). In more moderate regions, the additional cost of the ERV compared with the HRV may not be a cost-effective investment.
The ERV is discussed in detail as a separate measure (ET #461 Energy Recovery Ventilator with Heat and Membrane Humidity Exchangers for Commercial Application).
The standard practice is to exhaust outside ventilation air to the outdoors to maintain the design building pressure balance as the required outside air is supplied. Exhausting the ventilation air to the outdoors wastes the energy that was used to cool or heat that air when it was supplied to the building by the heating, ventilating, and air conditioning system.
This technology has been widely available for many years, but has not seen widespread adoption in the Pacific Northwest.
Preconditioning outside air reduces the load the HVAC unit must handle, which reduces the required capacity of the mechanical equipment (Hoger, 2009) so the installed equipment can be smaller. Because the HRV provides savings for summer cooling and winter heating operations, it can reduce both summer and winter electrical peak load demand charges (Hoger, 2009).
End User Drawbacks:
For retrofit applications, the exhaust air duct must be located close to the fresh makeup air intake (Kurt Roth, 09/17/2009). (At the same time, designers do not want the air intake to re-entrain the exhausted air.) Runaround coils may be used when the exhaust and outdoor airflows are separated by large distances.
A potential barrier to the widespread adoption of this technology is the lack of experience in the design community to properly design HRV systems. It is also important that these systems are properly modeled to accurately predict energy savings and integrate HRV controls with economizer operation. Introducing a heat exchanger into the ventilation system increases fan static pressure and, therefore, takes more fan energy, which will reduce the total savings of the technology. In mild climates with low fuel costs, the heating or cooling savings from heat recovery are partially consumed by the equipment costs and the additional energy used due to the increased fan loads. Therefore, the cost effectiveness in each application and climate should be examined carefully before installation.
Operations and Maintenance Costs:
Filters and possibly belts in the HRV will need to be maintained.
The HRV equipment is simple and has few components. With proper maintenance, the life expectancy should be more than 20 years.
Packaged HVAC systems with economizer heat recovery.
Reference and Citations:
Energy Saver 101: Home Energy Audits
U.S. Department of Energy
Heat Recover Ventilator
Carrier Heat Recovery Ventilator
Carrier HRV High Efficiency HRV
Fantech Commercial HRV
Heat Recovery Ventilator
Links to many sources
Roth, et. al.,
Energy Consumption Characteristics of Commercial Building HVAC Systems Volume III: Energy Savings Potential
Prepared by TIAX LLC for the U.S. DOE Building Technologies Program
Total Pacific Northwest Building Stock Based on Preliminary Numbers from the 2013 Update to the CBSA
Northwest Energy Efficiency Alliance
Northwest Commercial Building Stock Assessment (CBSA): Final Report
Prepared by the CADMUS Group for the Northwest Energy Efficiency Alliance
ERV is the Word