Cold Weather Heat Pump Charging

Checking the refrigerant charge of a heat pump in cold weather can be confusing for many technicians, at least partly due to the many different methods recommended by different manufacturers. Although there are many methods, most are described as heating performance charts or heating cycle check charts. A check chart is just that, a chart for CHECKING the charge during the heating cycle. It is not intended to be used for actually ADDING refrigerant. Why? Lower outdoor temperatures cause a lower evaporator temperature and pressure. Lowering the evaporator pressure increases the compression ratio, so the compressor capacity is reduced. Less refrigerant is being circulated in the refrigerant system because of the diminished compressor capacity at low outside ambient temperatures. The refrigerant that is not being circulated must sit somewhere, usually in the accumulator. For this reason, a charge which is adequate to maintain correct pressures and temperatures at 25°F may not be adequate at 35°F. How? Suppose that the unit was undercharged according to the check chart. If you add just enough refrigerant to bring it up to the required pressures, you have only added enough refrigerant for correct operation at that one condition. When the outside temperature rises, the unit will be capable of pumping more refrigerant. However, since you didn't add any extra refrigerant, there won't be any more to pump. The system will be undercharged. Just adding a little extra is not a great ida either because you really have no way to determine how much extra to add. This is why manufacturers say that the check chart cannot be used to CHARGE the system, only to check its operation. If the system is undercharged, the recommendation from many manufacturers is to recover the refrigerant in the unit and weigh in a total system charge according to the manufacturer's instructions. 

Thanksgiving 2011

Once again, Thanksgiving is here and I have so much to be thankful for its hard to know where to start. My family is doing well, my children are achieving and prospering, and my HVACR program has so many students that we have had to work really hard to meet their needs. All the Air Conditioning instructors at Athens Tech have really stepped up their game. Dennis Payton, Coleman Simmons, Gary Manley, Jack Parsons, Gene Smith, Bill Ely, and Kenneth Harris have done a stellar job this semester. I know that our students are fortunate to have the dedicated and talented instructors that I am fortunate to work with. We are coming to the end of our first semester since our system switched from quarters to semesters, and the transition has been smoother than expected.

I know that there are still far too many people without work and that the hard times have boosted our enrollment as people look to invest in their future. Our job as teachers is to insure that they have made a wise investment. We are preparing our students to answer the call when opportunity knocks. How many stories have you heard about someone being successful because they were in the right place at the right time? There is another part of their success that often goes unmentioned: they were prepared to answer when opportunity knocked. That is what students all across America are doing today – preparing for opportunities to come. Schools are bursting at the seams. We are planting the seeds of tomorrow’s success. I truly believe that a better educated, better trained pool of workers will propel our country into a time of prosperity in the coming years. Times will get better, opportunity will knock, and our students will be thankful that they were prepared to answer the call.

80% Furnace versus 90% Furnace

This week I would like to follow up on the 80% versus 90% debate. The primary argument for installing an 80% furnace is the lower cost of the equipment. However, a colleague of mine suggested that there is really not much difference in the installed cost because of the difference in the cost of the vent pipe. Standard B-vent is far more expensive than the PVC that is used in 90% furnaces. If the furnace is in a crawl space or basement, the 80% furnace must be vented through a chase or closet while the 90% PVC vent can usually be run sideways out through the wall. This also saves on labor. His argument is that the extra cost associated with installing a Category I furnace vent eats up the difference in cost between an 80% furnace and a 90% furnace. 

For a changeout, the math will favor an 80% furnace because there is already an existing vent. However, check to see if the vent is adequate. You may need to make improvements to the existing vent for the furnace to operate safely. Often, a fan assisted replacement furnace will use a smaller vent than the older natural draft furnace it is replacing. It is possible for the old vent system to be too big, causing condensation inside the vent which leads to rapid vent corrosion. Many older natural draft furnaces are vented into masonry chimneys, a practice that is usually discouraged when applying fan assisted furnaces. Several manufacturers require a metal flue liner for the masonry chimney, eating up most of the cost savings. Another common practice in older furnaces is the use of single wall vent connector. You really don’t want to connect a new fan assisted furnace in a cold location to a single wall vent connector, especially not an old one. I have seen single wall vent connectors rust through and fall on the ground in less than a year after installation of a new fan assisted Category I furnace. Again, replacing the old vent connector eats up some of your savings.  

It is true that there is still quite a cost difference between an 80% single stage furnace with a PSC blower and standard controls versus a 90% two stage furnace with an ECM motor and communicating controls, but the cost difference has more to do with the improved blower and controls. For a true cost comparison, both furnaces should have similar blowers, staging, and control systems.

Appliance Energy Efficiency Standards

The Federal Department of Energy, DOE, has issued a direct final ruling making on furnace and air conditioner efficiency. The regional efficiency standards ruling went into effect October 25. The country is broken into three regions: North, Southeast, and Southwest regions. A map can be seen at MAP. Read more about the ruling at RULING.

In a nutshell: in the Northern region furnace efficiency will increase while heat pump and air conditioning efficiency will remain the same; in the Southeastern and Southwestern regions furnace efficiency will remain the same while heat pump and air conditioning efficiency will increase.

The table below listing the changes comes directly from the final ruling.

Table I.1 Amended Energy Conservation Standards for Furnace, Central Air Conditioner, and Heat Pump Energy Efficiency

Residential Furnaces*
Product Class	National Standards		Northern Region** Standards
Non-weatherized gas	AFUE = 80%		AFUE = 90%
Mobile home gas	AFUE = 80%		AFUE = 90%
Non-weatherized oil-fired	AFUE = 83%		AFUE = 83%
Weatherized gas	AFUE = 81%		AFUE = 81%
Mobile home oil-fired‡‡	AFUE = 75%		AFUE = 75%
Weatherized oil-fired‡‡	AFUE = 78%		AFUE = 78%
Electric‡‡	AFUE = 78%		AFUE = 78%
Central Air Conditioners and Heat Pumps†
Product Class	National Standards	Southeastern Region†† Standards		Southwestern Region‡ Standards
Split-system air conditioners	SEER = 13	SEER = 14		SEER = 14 EER = 12.2 (for units with a rated cooling capacity less than 45,000 Btu/h) EER = 11.7 (for units with a rated cooling capacity equal to or greater than 45,000 Btu/h)
Split-system heat pumps	SEER = 14 HSPF = 8.2	SEER = 14 HSPF = 8.2		SEER = 14 HSPF = 8.2
Single-package air conditioners‡‡	SEER = 14	SEER = 14		SEER = 14 EER = 11.0
Single-package heat pumps	SEER = 14 HSPF = 8.0	SEER = 14 HSPF = 8.0		SEER = 14 HSPF = 8.0
Small-duct, high-velocity systems	SEER = 13 HSPF = 7.7	SEER = 13 HSPF = 7.7		SEER = 13 HSPF = 7.7
Space-constrained products – air conditioners‡‡	SEER = 12	SEER = 12		SEER = 12
Space-constrained products – heat pumps‡‡	SEER = 12 HSPF = 7.4	SEER = 12 HSPF = 7.4		SEER = 12 HSPF = 7.4

The increased standards will be phased in over a period of years. Compliance with the standards in the direct final rule will be required on May 1, 2013 for non-weatherized furnaces and on January 1, 2015 for weatherized furnaces and central air conditioners and heat pumps. Industry reaction has been split. AHRI helped to develop the standards and supports them. They want to avoid the confusion and cost that was associated with the 13 SEER efficiency change that gave the industry very little time to prepare. AHRI also points to the Canadian experience when they mandated 90% . Their sister organization, HRAI, has stated that there were very few problems with Canada’s implementation of 90% standards. Read the AHRI position at LETTER. 

ACCA opposes the standards, especially the 90% furnace mandate, concerned that the extra cost will drive customers to illegal contractors, who feel no compulsion to follow the rules and will cheerfully install equipment that legitimate contractors are not allowed to offer. read ACCA position at ACCA. 

HARDI also opposes the regional standards, citing the difficulty this will make for distributors who service two or more regions. Read HARDI position at HARDI. ACCA and HARDI also cite that there is currently no enforcement mechanism – no DOE police. Again, the problem is that contractors who don’t abide by the ruling achieve a competitive advantage over contractors who do. Regardless of how you feel about the ruling, this is now the law, and all of us in the HVACR industry should prepare ourselves. As far as the DOE police – be careful what you wish for!