New Refrigerants

I’m sending this with a big question on the new refrigerants that are out, such as R-410A. Am I being old fashioned in not wanting to accept them? Or, aren’t they just a little dangerous?

I know we have to move forward and be ozone friendly, but the pressures of R-22 or even R-12 are dangerous enough. As a tech, I think a lot of people will be hurt, if not killed, from ruptures — especially the young “greenhorns,” but also the experienced techs.

Do you think there will be a refrigerant to replace R-22 that may be closer in temps and pressures? It may not be a major deal once we get going, but I see a big danger right now. What do you think? Am I worried about nothing? I have been to a 410A class and there are still too many unknowns for me.

Answer: By Mark W. Spatz, P.E. Manager of Refrigerant Technical Services Genetron Refrigerants Honeywell Buffalo, NY

Are you being old fashioned? No, you’re smart to ask the question. Caution is always best when applying a new technology. However, you can’t judge the safety of a system purely by the refrigerant pressure. Any gas under pressure can be hazardous if the equipment used to contain it is not properly designed, or if technicians working on the equipment are not properly trained. The equipment we use for air conditioning and refrigeration applications has to meet rigorous safety standards, including pressure test requirements that subject the equipment to pressures three to five times the maximum operating pressure of the system. This means the equipment and tools you use for R-22, R-410A, or any approved refrigerant, have to withstand pressures well in excess of the pressures you would encounter even in extreme conditions. This same question was raised many years ago when the industry transitioned from R-12 to R-22. For example, at 75?F the vapor pressure of R-22 is about 70% higher than R-12 and technicians questioned whether the higher pressure of R-22 would result in more injuries. I think you know the answer to that one. Now we’re making another jump of about 65% at the same temperature, and the rules of having the right tools and training are still going to apply.

The answer to your second question on new refrigerants that have similar pressures to R-22 is that there are refrigerants (such as R-407C) that have pressures closer to R-22, but they have other disadvantages that keep them from wider-scale use.

The main reason why 410A has been chosen by most of the major air conditioning manufacturers in North America is that it is the most energy-efficient replacement available. The higher pressure and other properties of 410A (viscosity, thermal conductivity, etc.) allow oem’s to design more compact systems for a given energy efficiency rating. This means less copper, refrigerant, and steel.

We all know about the energy crisis occurring in California, but the energy efficiency issue will become even more important when our government raises the minimum energy efficiency or SEER level for residential equipment by 20% or 30% in 2006. R-407C and most other similar blends are actually less efficient than R-22, and won’t get us where we need to go.

In addition, 410A acts much like a pure fluid or azeotrope with a temperature glide of only one or two tenths of a degree, compared with a temperature glide of approximately 10? for 407C. This means 407C and many other high-glide blends will change composition or “fractionate” to some extent when you transfer them or when a system leaks. In plain English, that means some components of the gas will transfer or leak out faster than other components, and so after a slow leak or after several transfers, the refrigerant has the wrong percentages of each component. This may affect system operation and performance. R-410A doesn’t have the fractionation problems that higher glide blends have, so you don’t have to worry about topping off a system after a leak has occurred and been repaired.

As R-22 is phased out, there will likely be products such as 407C that have a pressure-temperature relationship similar to R-22, but P-T isn’t the whole picture, and we don’t expect to see any new refrigerants that meet the overall needs of the industry as well as 410A.

You mentioned the unknowns out there in the field, but there are actually hundreds of thousands of 410A systems operating in the U.S. and around the world today, and feedback from equipment manufacturers and the technicians who are used to working with 410A has been overwhelmingly positive. As the inventor and leading producer of this refrigerant, Honeywell has worked with manufacturers and industry organizations for more than 10 years to address the safety and application issues, so our industry can smoothly and safely transition to 410A. That transition is in full swing now, and 410A can be installed and serviced just as safely as the refrigerants we have grown accustomed to.

Residential Unit

I installed an Armstrong air conditioner with a 2.5-ton condenser. I also installed a 2-ton cooling coil, horizontal application. The house temperature from morning until about 2 p.m. will match the set temperature of the thermostat. However, by mid-afternoon the house temperature will rise to 80 degrees F while the set temp calls for 68 degrees. This is an upstairs apartment with the furnace in the attic with about 50 ft of line set. How do you determine which orifice to use?

Answer: By Jeff Rife Manager of Distributor Services Armstrong Air Conditioning Inc. Columbus, OH

The information you provided tells me that the problem is most likely caused by one of two things. It’s probably either a system operational problem (unit not performing correctly) or a situational problem (the unit’s application and load).

You must decide in which direction to proceed. The best thing to do is to start by gathering all the information and data you’ll need and determine which way to go from there.

If the measurements you take reveal that a system operational problem is preventing the unit from performing to capacity, then you need to address the area of noncompliance within the air conditioning system. If, on the other hand, the data you collect suggests that the system is actually performing to capacity, then you need to go in the other direction, looking to the application and load for the answer.

It appears your system may be working correctly up until a certain time of day. The first thing that must be done is to determine if the system is operating correctly during the time it will not maintain the conditioned space.

You should start by verifying that the correct orifice and refrigeration charge is being used. The required orifice size can be determined by checking the orifice-matching chart located in the condensing unit. Compare the model numbers of the condenser and the indoor coil used. The indoor orifice size is critical due to the fact that it is a fixed metering device. As the outdoor high-side pressure increases with higher ambients, the flow rate through the fixed metering device also increases. As the outdoor ambient increases, superheat levels drop.

The line set length will also affect refrigerant charge. The recommended additional charge is 0.6 oz/ft of 3/8-in. line over 20 ft of line set. (This is assuming the original factory charge has not been removed or changed.) If the charge weight of the system is questionable, it is best to start back at square one and weigh in the charge. The formula to use for the proper system charge is: unit recommended charge plus 0.6 oz/ft over 70 ft of 3/8-in. liquid line.

Once the system has run for at least 15 min, measure the following:

If it is the latter, I would look more closely at load calculation, focusing on window types and shading, wall materials, values, roof materials, insulation integrity, infiltration, internal gains, occupant numbers, and design criteria location. Small errors in any of these areas can throw off calculations substantially. Insulation R-factor of the duct insulation and duct leakage are two additional areas that can also dramatically affect the load.

If the sizing was done strictly based on square floor area alone, the calculation could be grossly undersized, especially in older, less-efficient homes.

When calculating system capacity in the field, several methods are available to give you an approximate figure. ARI standard 210/240 specifies indoor test conditions of 80 degrees F drybulb and 67 degrees wetbulb temperatures.

Naturally, the chance of a residence being precisely at 80 degrees/67 degrees is unlikely. To adjust for this, you can use a multiplier to account for the variations of the indoor and outdoor conditions. (See Table 1 to find the correct multipliers to use.)

Use this formula to calculate capacity: rated capacity x outdoor factor x indoor factor = capacity (new condition).

To test the capacity calculation further, you could do a latent heat removal calculation. Run the unit for 15 min until equilibrium conditions are reached.

Following that, run the unit for 1 hr continuously while collecting the condensate from the evaporator coil and weigh for net weight. Use this formula to figure latent heat removal: condensate (lb) x 1,060 = latent Btuh. (To save time, run a 1/2-hr test and multiply by 2.)

Line set sizing will also affect system capacity. Pressure drop is created by the line set length and by the weight of the column of liquid in a vertical riser. For every foot of vertical 3/8-in. line, you lose 1/2 psi.

What this means is that it is possible to reach a point where the pressure of the liquid refrigerant falls below its saturation temperature. This will cause the liquid to flash to vapor to cool the liquid to the new saturation temperature, resulting in capacity loss.

Using 3/8-in. and 7/8-in. line should be sufficient for 50 ft. But the number of elbows, line size, and vertical rise must all be factored in.

You always have to keep in mind that any variation from the rated conditions will affect capacity. Until you pin down all of your conditions, you can’t eliminate all the “could be’s.”

Humidity

A letter from Joseph Bebout in the May 14, 2001 Service Hotline asked about methods to cope with humidity. To add to the answer given, I’d suggest dehumidification to solve humidity problems. Dehumidifiers are available that dry out a place and provide some free reheat.

Air conditioning removes 1.5 lb per kWh plus reheat cost. High-efficiency dehumidifiers removed 5 to 6 lb per kWh and provide 1,200 Btu free reheat per pound of water removed. This also prevents overcooling of a facility, as well as condensation in the walls, ducts, and grilles.

Publication date: 12/03/2001