The author says that one divides the HSPF by 3.413 to get a heat pump's seasonal Coefficient of Performance. By this figuring, an air source heat pump just in compliance with US standards (HSPF of 6.8) will have a COP of 1.99. Many air source units have significantly higher ratings than this. Yet in Table 2 (p. 30) the article claims that the typical seasonal efficiency of an air-source unit is 150% (COP of 1.5). Why not provide a range of efficiences, starting with the legal minimum, as you did with just about every other technology?

Even worse, the article puts the typical seasonal efficiency of a ground source heat pump at 260% (COP of 2.6). Again, this is about the absolute worst one can do with this technology on a seasonal basis. Most units sold have COPs well over 3, under an ARI test regime that measures not seasonal, but winter peak performance. A 1993 EPA report found that standard ground source units with single-speed reciprocating compressors operated at a seasonal efficiency of 275% or better in the coldest U.S. climates, even taking into account the air handlers! In warmer climates, seasonal efficiencies weighed in as high as 500% for the best systems.

The panel Integrated Systems for Space and Water Heating mentions only gas systems, neglecting to mention integrated air- and ground-source heat pump systems that provide full-demand water heating. You also never mention the fact that most ground source systems are installed with desuperheaters, which can provide 15%-40% of a home's water-heating, essentially for free. Ground source systems also heat water while cooling the house.
 

Author Skip Hayden responds: I have nothing against heat pumps. In fact, with low electric prices, new efficient heat pumps can be an attractive option. I provided typical efficiencies of existing equipment, not rated efficiencies of new equipment. Notice that the article uses 60% as a typical efficiency for a gas furnace, although current standards are much higher. Heat pump efficiency is complicated because colder climates reduce efficiency. But a range-as we discussed in the heat pump section-may have been more appropriate in the table. Converting HSPF to seasonal COP is probably the most useful simple way to compare heat pumps to other heating systems. New air source heat pumps generally have seasonal COPs of about 1.6-2.8, while new ground source heat pumps generally have seasonal COPs of about 2.4-3.5. New technologies such as larger heat exchanger surfaces, two-speed scroll compressors, and efficient variable-speed motor-fan sets are continually moving the HSPF and COP upwards.

You make a good point about heat pump desuperheaters used to heat water. They were left out of the section on integrated space and water heating systems by an editing oversight, but are an excellent application and improve the economics of heat pumps. I agree that cash flow calculations can be beneficial in convincing people to purchase efficiency measures, especially expensive ones like ground source heat pumps or even high-efficiency condensing furnaces. However, simple payback calculations are still useful for quickly comparing with other options.

Editor's note: Look for an article on ground source heat pumps in the next issue of Home Energy.
 
 

• Where can one obtain replacement anodes, especially the secondary type that fit in the hot water outlet port?
• Can you really get anodes out of old tanks? (I thought I would torque the welded fitting off the tank so I quit trying.)
• Have you measured the additional energy use caused by residential recirculation systems? (They seem popular in upscale houses.)

Russ Johnson
Northeast Utilities
Hartford, CT

Larry and Suzanne Weingarten respond: Yes, anodes really can be removed from tanks without breaking the welds or your ribs. Using a torque multiplier (a geared tool that trades speed for force), we've removed hex head anodes from nearly two thousand tanks without causing damage. The tool is expensive (around $400), but would be worthwhile if you plan on changing multiple anodes. The combination anode can be installed in the hot outlet with only a pipe wrench.

Locating replacement anodes can be as challenging as removing them from tanks. Usually all you'll get at hardware stores is a quizzical look. Even plumbing wholesalers may not have the anode you need. These mail-order sources should be able to supply you:

Gull Industries. Tel: (800)748-6286
Water Heater Rescue. Tel: (510)945-6286
http://www.well.com/user/geant

We have seen no firm figures on recirculation system energy use and believe there are too many variables to make such figures very useful. Minimizing the time hot water is in piping reduces opportunity for heat to escape, and the Metlund system addresses that need well. Next best would be a thermostat- and timer-controlled system.

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