building-scienceheader image
Helpful? 0

This Heat Pump Problem Is a Surprisingly Common Cause for High Electricity Bills

Sometimes, the cheapest way to save energy is to fix what's not working

Posted on May 28 2014 by Allison A. Bailes III, PhD, GBA Advisor

She lives in a small, simple house in southern Mississippi. It's only 1,700 square feet. Why then, she wondered, were her summer electricity bills running more than $600?

The house didn't have any energy-hog features like a swimming pool, and she didn't do stupid things like leave all the doors and windows open while she ran the air conditioner. What could it be?

She called her electric company, one of the co-ops in Mississippi, and they sent someone out to investigate. Utility companies get calls like this all the time, and they've learned from experience what most of the main causes of high bills are. When the utility investigator arrived at the house, he asked her to tell him anything she knew that might help him.

"Well," she said, "the air conditioner runs all the time, but the house won't even cool down to 80 degrees."

"Ah, that helps to narrow it down a bit." He went to work, and it didn't take him long to find the problem. He measured the temperature drop across the air conditioner coil and found that the air on the 'cool' side wasn't much lower than the air on the warm side. And both were much warmer than they should be.

OK, that could be a disconnected duct in the attic, he thought. A look in the attic, however, showed that wasn't the case here. Besides, a disconnected duct would increase the bill, but it almost certainly wouldn't quadruple it.

The electric resistance element is on all summer

His next step was to turn off the breaker to the electric resistance heat (a.k.a. strip heat) in the HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. system. This is basically a giant toaster inside the air handler. Heat pumps use it for supplemental heat. In some homes, it's used as the primary heat source. It's not cheap, though, especially considering that the same electricity going into a heat pump will yield two or three times more heat.

Anyway, the utility investigator turned off the breaker to the strip heat and watched what happened to the meter. In the summer time, turning off the strip heat should have no effect at all on how fast the meter spins because it shouldn't be running. Strip heat is for cold weather.

In this case, the meter went from spinning fast enough to saw wood to moving as slow as a horned passalus (photo below) going for a walk in the woods.

"Well, we found your problem, ma'am," he told her. "Your heating and cooling system was doing both at the same time, making you spend a lot of money to stay uncomfortable."

Thermostat wiring errors

This problem often results from a thermostat wired incorrectly so that the system kicks on the strip heat when it shouldn't. Since anyone can go down to the home improvement store or the Interwebs and buy a thermostat, a good number of these problems result from DIY jobs.

It seems crazy to think that someone wouldn't notice that the heat is running in their home in summer, but they don't feel heat coming out of the vents. That heat gets mixed with the cool air from the air conditioner. They cancel each other out, both using even more energy because they're fighting each other.

Got high electricity bills in summer that you don't understand? Check your strip heat.

Allison Bailes of Decatur, Georgia, is a speaker, writer, energy consultant, RESNET-certified trainer, and the author of the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard.


Tags: , , ,

Image Credits:

  1. Energy Vanguard

1.
Wed, 05/28/2014 - 22:03

I have a client...
by Curt Kinder

Helpful? 0

...who has DIY'd his thermostat exactly that way...TWICE!

It does make for very very effective dehumidification, though. In fact, so effective, that I deliberately temporarily tie the strip into compressor operation in cool mode to quickly dry minor indoor flooding incidents arising from heavy rainfall or interior plumbing failures. It costs an extra buck or so per hour to operate, but it works for fast drying without overcooling.


2.
Sat, 05/31/2014 - 10:34

Putative Pros (PP)'s
by danny gough

Helpful? 0

Its not always the homeowner. Every now and then the "putative pros" (PP) pull boners like this.

Back in February I investigated a high bill complaint in a home which had a heat pump with gas furnace back up. The scheme was to allow the heat pump to heat the house as long as it had the capacity. Then the 2nd stage gas furnace kicked in to finish the call.

Turns out the PP didn't configure the reversing valve correctly. So instead of heating the house, the heat pump ran in cooling mode. When the indoor temperature dropped 2 degrees below set point, the heat pump shut off and gas furnace energized to heat the space to set point. In other words, the thermostat set at 70 degrees, space drops to 69, heat pump energizes in cooling. Space drops to 68, heat pump shuts off and gas furnace energizes to heat the space to set point.

The homeowner said "I don't like heat pumps. They just blow cold air. The only real heat we get is when the gas furnace runs." Huh. Maybe the unit just needs some freon……...


3.
Mon, 06/02/2014 - 07:57

Edited Mon, 06/02/2014 - 08:00.

Heat Strips, Refrigerant Leaks and Delta T
by rjp :

Helpful? 0

Part of the problem is the equipment itself. A few dollars worth of LED indicators installed by the manufacturers would help by indicating what is on when. Modern thermostats have largely eliminated direct indication of emergency heat. High electric backup costs are most common in the cooler months when the heat pump has failed due to refrigerant leaks in substandard coils. Too many techs just add freon instead of fixing the leak and too many homeowners don't realize ac systems don't "use up" refrigerant. Again the manufacturers could provide a simple indicator for pennies by adding the refrigerant sight glass where bubbles mean low freon. For a high tech warning, installers can add thermostats that measure delta T across the coil and warn the homeowner of poor performance by measuring the output to the inlet temperature factored by outside temp and indoor humidity.

Honeywell Delta T
https://www.forwardthinking.honeywell.com/related_links/thermostats/pres...


4.
Mon, 06/02/2014 - 09:58

Heat pump vs "HVAC"
by Steve P

Helpful? 0

I'm a tiny bit confused by the terminology used here. I'm sure many standard home central AC units have these electric heaters, as do true heat pumps which "harvest" heat from even cold air to heat homes.

This doesn't really change the overall message of the article (Check the Obvious) but it sort of muddies the water for me on the correct use (if it exists) of AC and "heat pump". To me, an AC unit only cools and any toaster element is a supplementary addition. It's not a heat pump. A heat pump (again, my understanding) can work "both ways" and both cool and heat, with the heating much more efficient (depending on outside temp or water temp if used). A heat pump may also have a "toaster element" but that's only used as a last resort.

Reading the article again I see it's not the article which is the problem - it's the headline. The article is pretty obviously talking about a central AC with a supplementary heater. It mentions heat pumps only to point out they would be more efficient at heating. So the "Heat Pump Problem" in the headline isn't the problem described (it;s an "AC heater" problem) and may not even exist (I'm not sure how easy it might be to wire a heat pump up incorrectly).


5.
Mon, 06/02/2014 - 10:54

Putative Pros?
by mike Walling

Helpful? 0

Putative? you are too kind sir. How about ersatz pros? Those young men hired for $15-20/hr and sent out to "figure it out" while you get charged full rate. Dirty little secret of the home repair industry.

My advise: If you get a secretary when you call their office, hang up and keep looking for that guy who won't return your call. He is the one that knows what he is doing.


6.
Mon, 06/02/2014 - 11:26

Edited Mon, 06/02/2014 - 11:30.

Response to Steve P
by Martin Holladay, GBA Advisor

Helpful? 0

Steve,
You wrote, "I'm a tiny bit confused by the terminology used here."

In the southern half of the U.S., many homes have a split-system heat pump to provide both heating and cooling. Everybody calls these systems "heat pumps."

Some homes have a gas furnace for heat. They may also have an air conditioner for cooling. These cooling units are called "air conditioners," but they never include strip heat (an electric resistance element). Heat pumps include strip heat; air conditioners don't.


7.
Tue, 06/03/2014 - 07:16

Edited Tue, 06/03/2014 - 07:33.

Steve P
by rjp :

Helpful? 0

The article is about a heat pump that can a) do cooling and b) economically provides heat by reversing the refrigerant flow and c) rarely provides expensive heat with supplemental resistance heating coils ("toaster elements"). When supplemental electric resistance coils are installed in a heat pump, they are often called "emergency heat".

The author is describing a heat pump whose controls have failed in the worse way; the refrigerant flow is in cool mode while the emergency heat is also on, obviously not by design. Therefore the way to gain efficiency is to fix the heat pump controls. Where the author confused the issue was by immediately discussing a variation that some use where the refrigerant system is AC only and the resistance heat is the "only" hvac heat component. Generally that kind of system has the lowest capital cost and is not a heat pump. Again heat pumps almost always have a supplemental backup heat source that is intended for periods when it's below freezing or when the refrigerant system has failed completely. My earlier post suggests manufacturers could improve user's operational awareness of heat pumps through a few simple expedients.

Mike Walling also makes a good point that hvac techs often lack experience while the author correctly suggests that the described failure could be a simple miswiring of the controls, perhaps even by a do it yourself owner or handyman. Finally this kind of failure really is not that common as the headline suggests; failure of the refrigerant system is common. In the summer everyone knows when a system is not cooling; in the winter a heat pump's emergency heat can mask the issue until the electric bill arrives.


Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!