Energy Recovery Systems for Replacements and Retrofits

Posted on November 23, 2020 by Buck Nye
Due to the recent COVID-19 crisis, ASHRAE’s Technical Committee TC 5.5 issued an updated “Practical Guidance for Epidemic Operation of Energy Recovery Ventilation Systems” (dated 6/9/20).  In addition, ASHRAE formed an ‘Epidemic Task Force’ that has produced multiple guidelines to assist design professionals, servicing contractors, and building owners in addressing how to improve indoor air quality. Recently, the ‘Building Readiness’ guideline was updated on 10/20/20

In ASHRAE’s guidance: “Well-designed and well-maintained air-to-air energy recovery systems should remain operating in residences, commercial buildings and medical facilities during the COVID-19 pandemic.  This is because maintaining at least normal outside air ventilation rates, with proper temperature and humidity conditioning of the inside space, is important for maintaining health and combatting infectious (bio)aerosols.”1 

This article will touch on the correct design and application of energy recovery devices.  The two main focal points will be 1) how to reduce the amount of cross contamination of exhaust/return air into the outside/supply airstream, and 2) what are the implications if you increase the amount of outside air. It is the last of a three-part series that included filtration and dilution in response to the COVID-19 pandemic.

ASHRAE Standard 1060 “Performance Rating of Air-To-Air Heat Exchangers for Energy Recovery Ventilation Heat Equipment’ established certified performance ratings for different type of energy recovery devices. The standard defines ‘exhaust air transfer’ (EAT) as the amount of cross contamination from the exhaust/return airstream into the outside/supply airstream.  The rate of EAT is referred to as ‘exhaust air transfer rate’ (EATR). Below is a depiction of EATR in an energy recovery unit.

In general, the EATR is dependent on the amount of airflow in the two airstreams as well as the differential pressure between the two airstreams. During these times of the pandemic, one of the recommended methods to improving IAQ is by increasing the amount of OA. From the diagram above exhaust/return air from the space can be considered to not be as ‘clean’ as the outside air being brought into the space. Therefore, EATR entering the outside airstream would reduce the amount of outside air and therefore diminish the indoor air quality. Please note that depending on the level of contamination of the exhaust/return air, ASHRAE Standard 62.1 (Ventilation for Acceptable Indoor Air Quality) allows EATR to be up to 5% and 10% of the outside airflow.

The Building Readiness document has three recommendations to be incorporated into a ‘well designed’ ER system.  These three items are: 
  1. The supply and exhaust fans are located correctly for pressure control at the exchanger.
  2. Size the ERV for an appropriate velocity and air pressure drop.
  3. Specify appropriate seals and purges for the application.  
Each of these recommendations are means to meet the minimum ASHRAE 62.1 requirements for a) outside air ventilation rates and b) the 5 to 10% acceptable EATR levels. 

The TC5.5 document has recommendations on how you can EXCEED 62.1 guidelines while using an ER device. The two methods on how to further improve your indoor air quality are 1) reducing the amount of EATR and 2) increasing the amount of outside air.


One method to reduce the amount of EATR to negligible levels (as opposed to the 5% to 10% allowable by ASHRAE 62.1) is to specify an appropriate energy recovery device.  One such product with ultra-low EATR’s is Semco’s model #TC3 ‘True 3A’ Energy recovery wheel.  It has ASHRAE 1060 certified performance for an EATR of 0.045 % when properly applied. Semco’s true 3A ER wheel is available in multiple size up to 70,000 cfm; and can be applied singly, in self-contained units, or as retrofits of existing wheels. In addition to its low EATR, it also incorporates an anti-corrosion and anti-stick coating to reduce cross contamination. However, in these times of heightened IAQ concerns, its best feature is probably the fact that the wheel faces and transfer media contains an anti-microbial coating which actively limits microbial growth.   

To further ensure achieving ultra-low EATR’s during all operating conditions and not just at design airflows is to incorporate Semco’s Health and Safety Monitor Control System to their ERW. This system actively monitors the varying airstream temperatures and pressure while adjusting the speed of the ERW to ensure that cross contamination does not occur.Please contact your HCN salesperson for assistance in designing and applying Semco’s products.

A method to eliminate all cross contamination (or an EATR of 0.00) is to design an ER recovery system that has the two airstreams separated from one another. Two examples of this type of ER systems are 1) refrigerant based heat pipes and 2) a ‘Run-Around’ Loop that utilizes water or glycol. The refrigerant heat pipe system uses the heat of vaporization and condensation to transfer energy between the two airstreams. A ‘Run-Around’ loop places a hydronic coil in the two different airstreams and then has associated piping, pumping, and controls to transfer energy between the two airstreams. HC Nye represents both types of systems though Heat Pipe Technologies (HPT). Please contact your HCN salesperson for assistance in designing and applying HPT’s products.


Increasing the amount of Outside Air through an ER device is the other method to improve IAQ. Increasing the amount of OA beyond 62.1 ventilation rates could result in your equipment being even more oversized during minimum operating conditions. At all operating conditions it is important that you still maintain comfort conditions with respect to temperature and humidity levels. Please recall that the epidemic task force is asking you to consider designing and operating equipment at three very different conditions: 

  • with OA quantities greater than ventilation code minimums  
  • at minimum ventilation code rates 
  • at minimum operating conditions.  
At a minimum, you should specify equipment that can operate in a stable and accurate fashion at these three different points. In a packaged piece of DX equipment, it is desirable to provide these components:

  1. Compressors – two-stage, digital scroll, or inverter driven.
  2. Fans – direct drive with EC motors or VFDs.
  3. Space humidity – modulating hot gas reheat.
  4. Heat – Electric heaters with SCR control or gas heat (modulating or staged) .
These components also allow for the greatest flexibility for potential operating conditions.  Given that all these components are variable and operate both simultaneously and independent of each other (within limits), the control system must be robust enough to accommodate the diverse operating points with diverse operating sequences.  We recommend that these controls should be factory installed.

In the ‘Overall System Considerations’ in the TC5.5 document, the first recommendation is to evaluate if your existing ER system can accommodate this increase. Packaged DX equipment located on a roof is the most common type of ER system installed today. Most of these ER systems are installed where there is recirculation of the return air from the space. Please see the diagram below that depicts an ER unit with recirculated air as well as an ER device for the outside air.

Providing a solution to increasing airflow across the heat wheel are the Aaon model RN and RZ rooftop units - available from 6 to 240 tons. For each of the different cabinet sizes there are two (2) different sized ER wheels available, a ‘small’ or ‘large’ face area. Each of the wheels has different maximum airflow available, however, in each instance the height and width of the two airstreams remains the same. If one wants to increase the amount of outside air, there may be a situation where a ‘small’ wheel was previously installed but a ‘large’ wheel is now required. In these instances, it could be relatively easy to replace the wheel.  The wheel/cassette assembly would just be swapped out because the overall face area is the same. Please note that in some instances the depth of the wheel would change; and this would also have to be evaluated to make sure there is enough space.

Another method to reduce the EATR and increase the OA ventilation rate would be to evaluate the replacement of the existing ER device. In most instances these devices are an energy recovery wheel that recover sensible and latent energy. ER wheels come in many different types of construction, face areas, depths, air pressure drops, EATR’s, and thermal effectiveness.

HC Nye represents four (4) different energy wheel manufacturers that are available for replacement work. Each of these manufacturers have different strengths and weaknesses that could be investigated to determine the best possible solution. If you increase the amount of outside air you would have to also consider the following items:

  1. Can the existing fan and air distribution system handle the higher internal APD?
  2. Can you still maintain comfort conditions for space temperature and humidity?
  3. Are you still maintaining the necessary air pressure relationships? Do you also have to increase the amount of exhaust air (EA)? 
Prior to COVID-19, two of the industry’s driving forces were energy conservation and Indoor Air Quality (IAQ).  Sometimes these two forces were at odds.  Ventilation rates had been decreasing over time and energy recovery had been mandated by codes adopting ASHRAE standards.  Now with ventilation rates precipitously increasing as a reaction to the pandemic, ASHRAE has provided guidance on energy recovery systems. 

For almost 40 years HC Nye has been a strong advocate for indoor air quality and has many products available to assist the HVAC community.  Your H C Nye sales engineer will be glad to assist as your address your IAQ concerns.
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ASHRAE Epidemic Task Force Recommends Increased Ventilation

Posted on October 14, 2020 by Buck Nye
Due to the recent COVID-19 crisis, ASHRAE has created an ‘Epidemic Task Force’ that has produced multiple guidelines to assist design professionals, servicing contractors, and building owners in addressing how to improve indoor air quality. Two of these documents are ‘Building Readiness’ updated 9-30-20 and ‘Schools and Universities’ updated 10-7-20
ASHRAE states: “The Building Guidance clearly encourages building operators to increase their systems outdoor air ventilation to reduce the recirculation air back to the space.”1  System design, outdoor and space conditions will each have a bearing on how feasible it will be to introduce more outside air.
This article is part 2 of a 3-part series that will focus on the design aspects of how to increase the amount of outside air which reduces the level of contaminants in the space. We will discuss some ideas for replacement work as well as suggest some potential retrofits of existing systems by adding energy recovery devices as well as other components.
1(ASHRAE Epidemic Task Force, Building Readiness, 9/30/2020)

One method to improve indoor air quality is to increase the ventilation rate of the outside air and to reduce the amount of recirculated air.  This strategy, however, creates tension for the designer trying to balance increased outdoor air (OA) with ASHRAE Standards 55, 62.1, and 90.1.  Increasing OA to an existing system can also create problems for contractors and building owners as comfort, cleanliness, and energy efficiency may suffer.

New or Replacement Applications

On page #17 of the ‘Schools and University’ guideline recommends increasing OA when a) retrofitting or replacing an existing AHU or b) if a dedicated outdoor air systems (DOAS) is being replaced.  The recommendation is for the designer to consider increasing capacities beyond code minimum for ventilation. This increase in the amount of outside air could drastically increase the capacity requirements of the heating, cooling, and dehumidification systems. This increase could also trigger the requirement of an energy recovery device to satisfy ASHRAE 90.1 standards.

It is H. C. Nye’s recommendation that when considering equipment replacement (AHU, RTU, or DOAS) that the designer or contractor should select equipment components that will allow stable operation at three design points: a) in excess of ventilation code minimum, b) at ventilation code minimum should the situation allow at a future date, and c) minimum operating conditions.  Furthermore, energy and comfort standards need to be met.   

As can be seen, a very broad operating envelope is required.  Such equipment should include the following:

  • 2-stage, digital scroll, or inverter driven compressors
  • Direct drive fans with EC motors or VFDs
  • Hot gas reheat with modulating control
  • Energy recovery devices (wheels, plates, coils)
  • High turndown modulating gas heat
  • Electric heaters with SCR control

Given that all these components are variable and operate both simultaneously and independent of each other (with limits), the control system must be robust enough to accommodate the diverse operating points with diverse  operating sequences.  We recommend that these controls should be factory installed.

Aaon’s broad range of products can provide all the preceding features, plus many more, including IAQ, special materials, high filtration, and acoustical packages.  Aaon’s products are uniquely qualified to increase the amount of outdoor air ventilation while still controlling space temperatures and humidity to ASHRAE 55 standards. Their products are designed with capacity control features that can hold tight temperature and humidity setpoints at the three referenced unique operating conditions. Furthermore, they can be selected to meet present and future ventilation requirements, with and without energy recovery devices.  In addition, many of Aaon’s products can incorporate an airside heat pump that will provide energy savings and superior temperature control when there are mild ambient temperatures. 

Evaluating Existing System’s Ability to Increase OA in Lieu of RA 

For existing systems where the OA and return air (RA) mix, an evaluation should be made to determine whether there is excess cooling and heating capacity available to accept an increase in the amount of outside air.  A “back of the envelope” calculation yields the following results and observations:

Download these evaluations in text format.

Increased Capacity with the Same Footprint 

As expected, increasing the amount of outside air results in larger capacity requirements. But what does that mean if you have existing equipment that you want to replace, is there any way to minimize replacement costs? One thing to keep in mind is that oftentimes HVAC equipment comes in a few different capacities for the same cabinet size or footprint. Some examples would be a 1000 cfm unit ventilator (U)V might be the same size as a 1250 cfm unit; a 200 cfm fan coil unit (FCU) may be the same size as a 400 cfm unit. Another example would be Aaon’s AAON’s model #RN packaged RTU, ERU and DOAS units that were designed with 6 different cabinet sizes. Within the same cabinets there are units of multiple tonnages that all have the same dimensions. As an example, Aaon’s AASON’s ‘D’ size cabinet has the same footprint and height for a 26 ton unit all the way up to 70 tons. Some of the models that are close in size have very little difference in weight and electrical requirements between them. Please note that any of these replacements would require a proper engineering evaluation to determine what other potential problems these changes may cause.  Please work with your H.C. Nye Sales Engineer to determine equipment capabilities and any impact on an existing system.

Retrofit with Energy Recovery 

Another option available to provide additional outside air for replacement work or retrofits would be to install an energy recovery (ER) device. ER wheels, plates, and coils recovery waste energy (sensible only as well as total) to pre-treat the outside air. This device would allow increases in the outside air quantity, would assist in maintaining comfort conditions and would help minimize the additional energy usage. 

H.C. Nye represents well know energy recovery manufactures,, such as AirExchange, NovelAire Technologies, Renewaire, and Semco. Each of these manufacturers have a variety of different ER products that are AHRI 1060 certified for performance and are available for retrofits, replacements, and new construction.

Pressurization Monitoring 

In instances where the amount of outside air can be increased, the ‘Building Readiness’ guideline on page # 18 also notes that building and space pressurization should also be evaluated. Existing exhaust and relief air systems might have to be changed to prevent additional problems, , such as doors not closing, excessive noise, and reverse of intended pressure required for a space.

H.C. Nye represents Paragon Controls Incorporated, a leading designer and manufacturer of airflow and pressure sensing systems for commercial and industrial applications. All of Paragons products are ISO 9001 certified for quality management, and are available for retrofit work as well as for new construction. Their airflow sensing elements and transmitters are available for installation for outside air, fan inlet as well as duct mounting. Their pressure sensing elements and transmitters are available for rooms and spaces, for outdoors, as well as duct mounting. 

In conclusion, ASHRAE’s Epidemic Task Force has determined that increasing the amount of outside air to a space would increase the indoor air quality in these times of the COVID-19 crises. They have addressed some of the methods that are available, while also emphasizing that temperature and humidity conditions must still be maintained. For almost 40 years H.C. Nye has been a strong advocate for indoor air quality and has many products available to assist the HVAC community.

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Improving Indoor Air Quality for New, Replacement, and Retrofit Work.

Posted on September 22, 2020 by Buck Nye

Due to the recent COVID-19 crisis, the HVAC industry has pivoted towards improving indoor air quality for occupants in buildings. Indoor air quality incorporates three strategies to manage the indoor environment: source control, filtration, and dilution. 

ASHRAE has recently created an ‘Epidemic Task Force’ to help deploy ASHRAE’s technical resources to address the challenges of the current pandemic. They have produced two guidelines to assist design professionals, servicing contractors, and building owners on how to improve indoor air quality. The documents are ‘Building Readiness’ dated 5-21-20 and ‘Schools and Universities’ dated 7-17-20. These guidelines strive to:

  • Increase the filtration
  • Increase the amount of outside air being delivered to the spaces
  • Still maintain space temperature and humidity conditions.
This article is part 1 of a series of 3 articles that will touch on some of the items discussed in the two task force documents. We will focus on the retrofitting of existing equipment and designing of new or replacement equipment. Part 1 will discuss source control and filtration.  In successive weeks, part 2 will discuss dilution and part 3 will discuss energy recovery and other system implementations. 

Part 1 – Filtration & Source Control:

For upgrading and improving filtration the task forces recommend that the mechanical filter efficiency be increased to as high as possible. One should strive for a MERV 13 rating and preferably MERV 14 or better. Increasing the filtration effect to MERV 13 or higher would help reduce the transmission of infectious aerosols as these types of filters are better at removing particles in the 0.3 to 1.0 micron range, the size of many virus particles. However, be careful!  The increase in filtration will result in:

  • Higher air pressure loss
  • Reduce system airflow
  • Increased energy consumption
  • Increased likelihood of temperature and humidity problems in the space.

Complexities of Increasing Filtration

The  ASHRAE guideline has very detailed instructions on how to evaluate the ability to increase the MERV rating in a HVAC unit. Some of the tasks they recommend performing are:
  • Collect and record data on the existing equipment. 
    • Some of the information would be: 
      • Heating, cooling, and dehumidification capacity
      • Filter sizes and MERV ratings
      • Fan curves/performance
      • Type and size of motors and VFD’s
      • Size of electrical service, etc.
    • Hire a qualified testing, adjusting and balancer (TAB) agent to perform and document a complete temperature and static pressure profile of the existing equipment prior to any filter upgrades.
    • Perform an evaluation of the ability of the existing system to accept an increase in the MERV rating. Some examples of the tasks required would be:
      • Can the existing filter racks accept a thicker filter, if not, can the rack be modified?
      • How does the increase in air pressure drop effect the loss of airflow? 
      • Is enough heating, cooling, and dehumidification still provided at the lower airflows?
      • Does the fan and motor have to increase in size, if they do, is there enough physical space within the unit, is a larger electrical service required? 
    If MERV 13 filters cannot be installed; consider some of the following alternative solutions:
    • Increase the filtration to the maximum available.
    • Provide recirculation fan filtration unit.
    • Provide separate HEPA filtration unit.
    • Consider alternate filter locations, but once again evaluate the implications associated with the higher static pressure loss.

    Air Ionization A Simpler Solution

    Air ionization such as provided by Global Plasma Solutions (GPS) can result in a much simpler, quicker, and more cost-effective solution to the process outlined above on how to increase filtration. Studies have been performed that demonstrate how a MERV 8 filter with the addition of a GPS bi-polar air ionizer is equivalent to the filtration effect of a MERV 13 filter. A copy of this study can be downloaded here

    Adding a GPS device to your existing MERV 8 filtration system versus upgrading to a MERV 13 filter will result in:

    • No reduction of airflow
    • No reduction in your heating, cooling and dehumidification capacity
    • No additional energy usage
    • No loss of temperature and humidity control in the space. 

    GPS products improve indoor air quality by reducing particles, odors, and pathogens. GPS products are made with flexibility in mind and are available for installation in AHU’s, RTU’s, FCU’s, WSHP’s, DFS, VRF, etc., as well as for ductwork. The units are inexpensive, easy to install, and require very little maintenance. Unlike other air ionizing manufacturer’s, GPS’s products are UL-867 and UL-2998 certified that they do not generate harmful ozone or other byproducts. Please contact your local HC Nye salesperson for assistance in selecting a GPS product that best meets the needs of your application.

    • Increase the filtration effect of HVAC equipment
    • Provide additional dilution by increasing the outside air quantities
    • Continue to satisfy indoor comfort conditions
    • Minimize energy costs.

    In each of the documents, to improve indoor air quality and to reduce the chance of the spread of infectious diseases, the task force has recommended the implementation of ultraviolet germicidal irradiation (UVGI) in the form of UV-C lights.  UV-C lights destroy microorganisms (viruses, bacteria, and mold) by destroying and disrupting their nucleic acids; the lights can be selected to destroy pathogens on the surface that it shines on, as well as to reduce and kill the air-borne pathogens that travel past its rays. 

    Another product that could be used to increase the filtration effect in an existing space would be to add a ‘Critical Environment Air Handling Unit’ that is manufactured by Magic Aire. This small, horizontal air handler includes a 2 stage MERV 8 and MERV 13 filtration system as a standard offering; there is also an upgrade available to provide a HEPA or MERV 14 final filter. The unit can provide supplemental heating and cooling for constant volume or VAV application. In addition to the high filtration, it has other indoor air quality features available such as double wall construction with an anti-microbial treatment, UVC lights, a double sloped drain pan, as well as full size access doors.

    In conclusion, ASHRAE’s Epidemic Task Force has done an excellent job in identifying ways to increase indoor air quality in these times of the COVID-19 pandemic. They have developed a thorough and accurate list of recommended items and ways on how to improve the filtration efficiency associated with HVAC equipment. 

    For more than 40 years HC Nye has been a strong advocate for indoor air quality and has many products available to assist the HVAC community. These products can:

  • Increase the filtration effect of HVAC equipment

  • Provide additional dilution by increasing the outside air quantities

  • Continue to satisfy indoor comfort conditions

  • Minimize energy costs.

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RuppAir Providing Reliable Healthcare Ventilation with Rapid Lead Times

Posted on April 13, 2020 by Buck Nye

RuppAir has FAST Shipping from 6 local Plants

If you are looking for healthcare ventilation solutions that you can get quickly, RuppAir has 5 products that have rapid lead times and are manufactured in 6 local plants.  Contact us at 717-561-2500 to discuss your project's specific needs. 

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Posted on April 6, 2020 by Buck Nye

AAON Going Above & Beyond

Tulsa manufacturing company is providing equipment for a temporary hospital in the New York City area, the current epicenter of the COVID-19 pandemic.

AAON, which makes large-scale heating and cooling units, is building 2,200 tons of HVAC apparatus for the Stony Brook Temporary Hospital. Stony Brook is on the north shore of Long Island, just east of New York City.

More than 1,300 people have died from COVID-19 in New York City, which is struggling to find hospital space to care for the critically ill.  Read full article from Tulsa World


From Gary Fields, AAON President
If you watched or listened to the WEBEX broadcast this past Thursday, I stated that AAON would go above and beyond to assist with fulfilling Emergency needs related to COVID-19. Further, I stated that AAON would provide expedited manufacturing and shipping at Standard multiplier, no Premium multiplier for these projects.  
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Coronavirus Prompts Response in HVAC Industry

Posted on March 13, 2020 by Buck Nye

Exerpt from an ACHRNEWS article:

One of the big questions about coronavirus — especially from an HVAC perspective — is how significant of a role airborne transmission plays in its spread. As professor of architectural engineering at the Pennsylvania State University and founding director of its Indoor Environment Center, William Bahnfleth, ASHRAE presidential member, is well versed in what’s been published recently on that topic.

“The current consensus is that it's predominantly large droplet transfer,” he reported. This means droplets too large to remain airborne that are spread through coughing and sneezing within a fairly close range of other people. The Center for Disease Control (CDC) puts this range at about six feet.

“If I were to cough or sneeze in your direction unprotected, some of the virus-containing droplets coming out of my mouth or nose might enter your mouth, eyes, or nose and cause an infection,” he said.

Another mode of transmission involves intermediate surfaces. For example, an infected person might cough or sneeze into their hand and then leave infective material on a door knob that someone else might touch and then transfer it to their own mouth or eye.

“But there's also the potential for airborne transmission,” Bahnfleth said. “And if viruses that are viable are in those droplets that you're producing, some of them will be small enough that they will stay airborne for a long time. So, it's not impossible that infectious particles in the air could stay aloft long enough to be collected, say at the return grille of an HVAC system, go through a duct, and infect someone in a different space.”

“Because there are three distinct ways of transmitting an infection,” he added, “even perfect control of airborne pathogens would not eliminate all risk.”
Read the complete article

Solutions For Airborne Pathogens

Ultraviolet-C equipment by UVR and Needlepoint Biopolar Ionization technology by GPS have proven track records with destroying airbourne pathogens.  Find out more about their solutions. 

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