                      A2/A3 Refrigerants in HVAC Products
                                  UL JTG WG1

This report is being issued by UL JTG WG1 (HVAC) to the UL JTG Executive Committee as recommendations relative to use of A2/A3 refrigerants in HVAC products covered by UL standards.  
The UL JTG WG1 is tasked with making recommendation for use of A2/A3 refrigerants in HVAC products covered by related UL standards.  Specifically: UL 60335-2-40, UL 484, and UL 474.
      (*) The WG can only propose changes and assist in drafting revisions in the standards.  Ultimately the standards must be revised by UL through the UL STP process.
Scope of Work  -  WG1 HVAC

      The scope of work is limited to safety requirements for use of A2 and A3 refrigerants with in the products covered by UL 60335-2-40, UL 484, and U L474.
      
            Requirements for A2L refrigerants in these standards will be addressed after IEC TC61/SC61D/WG9 completes their work. This work may start once WG9 reaches the CDV stage and the standards changes are reaching conclusion.

      UL 484 Scope:  (Generally free discharge, but may be ducted)
   *             Room Air-Conditioners (fixed appliance)
   *             PTAC (Packaged Terminal Air-Conditioners)  -  (fixed appliance)
   *              "Special purpose air-conditioners"
         o                   Spot Coolers (portable)
         o                   Computer Room units (portable if with wheels)
         o                   Enclosure Air-Conditioner  -  (data centers  -  fixed appliance)
   *             Recreational vehicle air-conditioners (fixed appliance)
   *             One on One mini-split. (non-ducted) 
      
      UL 474 Scope:
   *             Dehumidifiers.

      UL 60335-2-40
   *             Most air-conditioning products under 600v not covered by UL484 and UL474 are covered under UL60335-2-40.  Most over 600v products are covered by UL1995. 
   
   This report is structured in two sections.  The first section will specifically address UL 484.  The second section will address UL 60335-2-40 and U L474 (dehumidifiers).  
   

Executive Summary

WG1 recommends that the use of A2/A3 flammable refrigerants in HVAC products covered by UL60335-2-40, UL484, and UL474 should be limited by the following constraints:

   1. Refrigerant charge for any single refrigeration system shall not exceed; 
            m1 (kg) = 3m[3] * LFL 
   2. Refrigeration systems shall be limited to factory sealed appliances systems which are charged in the factory.  Note: factory sealed does not allow service valves for routine service. 
   3. If ducted, potential ignition sources shall not be installed in the duct.
   4. The temperature of surfaces which may be exposed to leaking refrigerant shall be limited to the refrigerant Auto Ignition Temperature (AIT) minus 100K.
   Note: Additional markings and instructions shall be provided.  These are detailed in marked up copies of UL484 SA and UL60335-2-40 and are available on request.


UL484  -  "Room Air Conditioners"  -  Report Section 1
Introduction
UL 484 and IEC 60335-2-40 currently contain requirements for flammable refrigerant charge limits based on m1 and m2 calculated based on the refrigerant LFL.  The m1 charge limit is based on unrestricted installation; while m2 charge limit is based on restrictions on room size.  The charge limit for charge levels m1 <M< m2, the maximum charge is based on the room area in an unventilated space (no mechanical or natural ventilation), making installed room area critical to safety for charges greater than m1.  

With the introduction of flammable refrigerants to the domestic residential and light commercial market place we must recognize the impact on the consumer, users, installers, inspectors, service personnel, and customers in retail establishments relative to the products being addressed. 

Because of a number of factors the committee recommends limiting the charge to m1 for domestic residential and light commercial application, including recreation vehicles.  

The factors considered were: 
 
   1. With regards to the consumer, the North American consumer market is transitioning from an environment with A1 non-flammable refrigerants to low GWP alternatives which may be flammable.  With non-flammable refrigerants it has not been necessary to consider the installed room area in the determination of safety requirements. With flammable refrigerants, a number of additional mitigation steps, including considering the installed area, will need to be considered for safety depending on the charge level.  

   2. Consumer purchasing today is based on cooling needs and affordability without giving consideration of room size for refrigerant safety.  It is common knowledge and well-documented that some consumers, due to their perceived understanding of the products, will install these products without consideration of the instructions and related safety documents.  It is expected that these practices will not change due to the use of flammable refrigerants.

   3. These products are considered appliances and are not controlled by building codes, are not subject to inspection, and are generally not installed by licensed HVAC technicians.

   4. Service personnel today are accustomed to working with non-flammable A1 refrigerants.  With flammable refrigerants additional precautions and training are required when installing and servicing.

   5. In the U.S. it is the common practice in northern regions to remove the room air conditioner from the window during the colder seasons.  Installing and removing a room air conditioner from a window each season increases the chance that the room air conditioner will be damaged such that leakage of the refrigerant could occur.  

   6. With the seasonal removal, a room air conditioner may be stored in a small room or closet, which may include ignition sources such as gas hot water heaters.  Although the room air conditioners are not operational during storage, the possibility for leakage still exists.  Such leakage within the small room or closet increases the risk of ignition based on the small room size. 

   7. Portable air conditioners are, by design, intended to be frequently moved from room to room on demand by the user.  Like window room air conditioners, they are also likely to be stored off-season in small rooms or closets.

Therefore, the JTG/WG1 determined that safety must be controlled by charge limit and cannot be based on installed room size and the expectation that minimum room areas requirements will always be complied with.  For this reason refrigerant charge amounts greater than m1 should not be allowed.

In addition, consideration must be given to the charge level limits for m1, in consideration of common installation practices and home construction, including room sizes relative to the air-conditioner.    

Previous work done by IEC TC61/SC61C concentrated on appropriate charge limits for refrigerators.  For determination of m1 in refrigerators a volume of 8 m[3] (2m by 2m by 2m) as a "small" kitchen area and a 50% safety factor (50% LFL kg/m[3]) was used for determining charge quantity limits:

      m1 = 8m[3] x 50% x LFL = 4m[3] x LFL
            Ref:  8m[3] = 2m x 2m x 2m (6.6' x 6.6' x 6.6')
      
(*) This equation yields 152 grams of R290 (propane).  IEC TC61/SC61C (IEC 60335-2-24 and 60335-2-89) rounded to 150 g.  
      
      Note 1:  This approach does not take into account pooling or stratification of heavier than air refrigerants.  However, this approach for determination of m1 limits has been globally accepted.
      

This equation was also accepted for determination of the m1 limits for HVAC products in IEC 60335-2-40 and ISO 5149; and is currently published in the Supplemental Annex to UL 484.

WG1 considered that room air conditioners are known to be installed and stored in smaller spaces than refrigerators and therefore a smaller volume should be used in the determination of m1.

It is common in the USA to find these products installed in rooms that are smaller than 8m[3].  Some examples are:

   * Airport parking garage attendant booth.
   * Toll booths 
   * Drive through coffee stations
   * Portable lunch canteens
   * Recreation vehicles.

The committee estimated the typical size of these applications may be as small as 4' x 8' x 6.6' or 5.94 m[3].  This was then rounded to 6 m[3]. 

Therefore, it is recommended that the determination of m1 for products in UL 484 be based on a volume of 6 m[3] (1.7m by 1.7m by 2m) as a "small" room, and using the same 50% safety factor (50%LFL kg/m[3]) for determining charge quantity limits.  The equation then becomes;

      m1 = 6m[3] x 50% x LFL 
--------------------------------------------------------------------------------
      m1 = 3m[3] x LFL
      Ref:  6m[3] = 1.73m x 1.73m x 2m (5.7' x 5.7' x 6.6')

Based on this equation the charge limits for select refrigerants are: 

Table 1
      
      (*) Charge limits apply to the largest single refrigeration circuit in the appliance.
As a check on the impact of our assumption on room size (6m[3]), the committee evaluated extreme cases of storage or operation in even smaller rooms. Utilizing this equation, the average concentration could potentially reach the following levels;

   * At a room volume of 4 m[3] the average concentration could reach 75% of the LFL
   (*) 4m[3] = 1.4m x 1.4m x 2m (4.6'x4.6'x6.6')
   * At a room volume of 3 m[3], the average concentration could reach 100% of the LFL
   (*) 3m[3] = 1.2 x 1.2m x 2m (4'x4'x6.6')

Although these products may be stored in such small rooms, with the m1 charge, the potential for a catastrophic leak reaching the LFL and a concurrent presence of an ignition source is unlikely.

As a reference, global experiential evidence is largely around 100g of A3 refrigerant (R290 or R600a) used in household refrigerators designed for flammable refrigerants is an accepted level of safety.  Although the use of refrigerators with flammable refrigerant in the USA is very small, this is not the case in Europe and Asia.  In these regions, refrigerators designed specifically for flammable refrigerants have been in the market place for over 15 years and over 100,000,000 household refrigerators using flammable refrigerants are in use with low level of incidents.

Published standards, IEC 60335-2-40 and ISO 5149 currently set charge limits of:

   * m1 = 4 m[3]*LFL (no area requirements)
   * m2 = 26 m[3] *LFL (with requirements for minimum area) 

However, for direct release air-conditioning products, no evidence could be identified of significant production of these products at charge levels greater than 100g of A3, with the exception of Portable Air Conditioners.  There are other products, such as EAHP (Exhaust Air Heat Pumps) which have up to 500g of R290 on the market, but these are indirect release systems.

Portable Air Conditioners with up to 300g of R290 have been in production for many years in the global market place.  The team looked for documented evidence of failures, however, could not find any formal mandatory reporting of fires and similar incidences that could be referenced.  In the USA we would reference CPSC, NFPA, and similar sources. In other countries, detailed fire incident reporting and collection of this data is not available to the same extent.

The UL JTG WG1 committee, at this time, is not considering differing values for maximum charge quantities for fixed appliances or stationary appliances within the scope of UL 484.  The committee fully recognizes that the maximum charges discussed in the portable appliance discussion above does not consider; a) potential mitigation factors that are more applicable for fixed or stationary appliances, b) the likely larger room volumes of those products, nor c) the extended flammable refrigerant properties and characteristics discussed in the "Future Considerations" section of this report.  As such, in the future the committee is open to considering a modification of the maximum charge quantities for fixed or stationary appliances given more analysis of such mitigation factors and applied room volumes.
Impact
Estimated average product capacity, based on proposed charge limits, for select refrigerants are;
Table 2
 Assumptions->   
      (*) Estimated capacity limits are based on a single refrigeration circuit in the appliance.
Notes: 
   1. The estimated average product capacity has been calculated on typical lbm/ton charge levels.  Actual lbm/ton charge will vary considerably with product design and technology.
   2. Technology exists to reduce the lbm/ton, such as micro-channel heat exchangers.  
   3. The capacity limit estimates are based on products with a single refrigeration system.  Dual systems would double the estimated capacity.
Additional Requirements
   1. It is recommended that use of A2/A3 refrigerants be further limited to:
         oo Factory charged
         oo Factory sealed systems (service ports for routine service and maintenance are not allowed)
      The critical to safety factor in these products is the charge level.  By limiting the use to factory charged, factory sealed appliances it places a much higher level of control on the installed charge and includes a factory leak test of the complete sealed system.  As such, the critical to safety factor in these products - charge level - is tightly controlled.
      Risk assessments for flammable refrigerants consistently identify servicing of the refrigeration systems as the highest risk activity.  Limiting the use of A2/A3 to factory sealed systems reduces the probability of a service related events.  It also increases the probability that if the refrigeration system is serviced, that it will be by qualified service personnel in a controlled environment. 
   2. Products such as PTAC's and A/C for recreational vehicles may include short ducts.  For ducted applications, the ducts shall not contain ignition sources.
   3. For products using flammable refrigerants, any surface temperature which may be exposed to leaked refrigerant (including auxiliary electric or fossil fuel heat) shall be limited to the refrigerant Auto Ignition Temperature (AIT) less 100K.  This applies to normal operation  -  not abnormal test conditions. (reference UL 484 SA 5.3.1) 
UL 60335-2-40  -  Report Section 2
JTG WG1 recommends that for the next revision of UL 60335-2-40 include the following revisions relative to A2/A3 flammable refrigerants.
   oo Include the requirements for products covered by UL484 Room Air-Conditioners
   oo Include the requirements for products covered by UL474 Dehumidifiers.
   oo And similar products covered by UL60335-2-40 to the extent that they comply with the same requirements and limitations  -  for example heat pump water heaters. 
The A2/A3 refrigerant safety requirements will be written to allow use of A2/A3 refrigerants in any factory sealed factory charged appliance.  Charge levels will be limited to m1 = 3 x LFL.  Charge levels greater than m1 will not be allowed.   These restrictions apply to direct release systems only.

These same requirements apply to dehumidifiers.  Flammable refrigerants are currently not allowed for use in dehumidifiers (UL 474).  Adding the above requirements to UL 60335-2-40, will now allow use of A2/A3 refrigerants in dehumidifiers up to m1 = 3 m[3] x LFL (114g R290).   The highest sales volume of products in the market, generally have charge levels under 120g of 410A (equivalent to ~60g ofR290).  The largest residential dehumidifier that UL has listed is has 305g R410A (equivalent to ~ 150g of R290) 
   (*) It should be noted that UL has received no requests to add requirements for A2/A3 refrigerants in dehumidifiers at this time.  

Requirements for A2L refrigerants in these standards will be addressed after IEC TC61/SC61D/WG9 completes their work. This work may start once WG9 reaches the CDV stage and the standards changes are reaching conclusion.

JTG WG1 will work to mark up UL60335-2-40 1[st] Edition (based on IEC 60335-2-40 4.2 Edition) with these changes and provide to CANENA WG2.  CANENA WG2 will update UL60335-2-40 1[st] Edition to harmonize with the IEC 60335-2-40 5[th] Edition, and IEC 60335-1 5[th] Edition to the greatest extent possible.  

It should be noted that UL60335-2-40 is a tri-national harmonized standard.  CANENA WG2 includes representation from USA, Mexico, and Canada with a goal of North American harmonization.  

Ultimately, all revisions to UL60335-2-40 are subject to approval by the UL STP.


Future Considerations
A2/A3 refrigerants by definition are flammable and can produce deflagrations. Like all flammable products, combustion involves direct and indirect heating of surroundings, consumption of oxygen and a pressure wave on ignition. ASHRAE and ISO have placed these flammable refrigerants into class by flammability properties and these classes show significant differences in their hazard potential.  At this point in our analysis all flammable refrigerants have been treated without consideration of these differences. This analysis sets the volume of flammable gas equal regardless of flammability classification.
We have not accounted for differences in flame properties, such as;
   * slower burning velocity ( slower kinetics)
   * higher MIEs
   * unstable flames (self-destructive rather than self-propagating)
   * large quenching distance
   * Incomplete combustion
   * lower severity and explosion damage
   * lower overpressure with minimal venting
   * increased flame thickness. Time scale of reaction closer to time scale of heat and mass transfer
   * lower (dp/dt)max (pressure rise)
As such, this approach is conservative and there may be room for additional discussion in the future with further considerations of available research and information.

