Letters: November/December 2005
I have a question regarding your article about inline or instant gas-fired water heaters (“Tankless Option Improving,” July/Aug ’05, p.18). Inline or instant gas-fired water heaters have a gas input of 135,000–195,000 Btu per hour, versus the standard storage water heaters, which have gas inputs of 35,000–40,000 Btu per hour. Since the instant water heaters are more efficient and have other attributes that make them attractive as replacements for storage water heaters, would greater numbers of the more efficient water heaters in a utility’s service area have an effect on the peak demand for natural gas?
Energy Information Center
Minnesota Department of Commerce
St. Paul, Minnesota
Author Dave Springer replies:
We have heard anecdotal concerns raised that high-capacity tankless gas water heaters may present a peak-load problem for some gas utilities. As you point out, peak gas demand may be 4–5 times higher than for a standard storage gas water heater. During winter months, when the cold winter inlet temperatures entering the tankless heater are at a minimum, morning showers are likely to be coincident with the peak space-heating load. We do not have any solid data on the magnitude of this potential problem. An assessment is needed to determine how significant an issue this may become as saturation levels of tankless gas water heaters increase.
I am a retired housewife living in Ball Ground, Georgia, about 50 miles north of Atlanta. My husband and I argue about fans all the time. I read an article from your magazine that said it’s better to turn off a fan when you are not in the room (“Ceiling Fans: Fulfilling the Energy Efficiency Promise,” Jan/Feb ’01, p. 24). When we lived in Marietta, I wired all the fans in the house so they would work independent of the lights. The fans ran 24/7 for close to 35 years. Here in Ball Ground, the fans are wired to switches separately. My husband is retired now and he follows me around turning off fans. We are going to disregard the fact that I am always hot and he is cold. Fans are always on when I am in the room, period. The problem arises when I leave a room.
We have our thermostat set at 77ºF or 78ºF in the summer and 68ºF in the winter. If the ceiling fan is not running and our air conditioner is on, doesn’t the cold air hit the thermostat that is located on the wall next to one of the vents, thus sending a message that the room is cool enough when it may not be? I am not talking about the windchill, just circulating air to keep the house at a constant temperature. I am only saying that not every house has enough vents or cold-air returns, and that they may not be located in a perfect spot. In some instances couldn’t it be beneficial to run the fans when you are not in the room?
Ball Ground, Georgia
Author and part-time marriage counselor Chris Calwell responds:
It is true that a ceiling fan can help reduce the stratification of air in an unoccupied room. This tends to have the effect of raising the temperature slightly in the first few feet of the room above the floor, instead of letting all the warm air collect near the ceiling. Alternately, if a room is being actively air conditioned, you can imagine the coldest air collecting near the floor, the warmest air collecting near the ceiling, and the air temperature a few feet above the floor being somewhere between the two extremes—roughly the same as the average room temperature if all of the air in the room were thoroughly mixed.
The Florida Solar Energy Center did some research a few years ago indicating that homes with central air conditioning in Florida tended to use more energy in total if they had ceiling fans than if they didn’t. Owners were leaving on the ceiling fans 24/7 while running the A/C, and did not raise their A/C thermostats higher to allow the resulting ceiling fan windchill to reduce air conditioner usage time. The total electricity use of the air conditioner and the ceilings fans, not surprisingly, was higher than the electricity use would have been for the air conditioner alone.
Your question could only be answered definitively by an auditor who inspected your home and measured the energy use of its various HVAC systems. My strong hunch is that you’re still better off switching off the ceiling fan whenever you leave the room. It sounds like your A/C system and its set of return ducts are providing reasonably good mixing in the room with the thermostat already, so it’s not clear that a ceiling fan could provide enough additional benefit to warrant its power use in an unoccupied room. The other option you might consider is replacing the fan with a thermostatically controlled Energy Star model—I’ve seen them sold at Home Depot in recent months. That way, the fan would only come on when the location where the remote control is sitting exceeds a particular temperature—whether the room is occupied or not.
Air Conditioner Question
I hope you can help me. I live in Colorado Springs, Colorado, in a house with 2,400 ft2 on the main level. My smaller air conditioner on the lower level is more than adequate, but the air conditioner on the main level runs continuously from around 11 am until we shut it off at 9 pm. I have a 2 1/2-ton air conditioner on the main level, but we have a house with its back facing west. Since we have nothing but windows facing west, the air conditioner just can’t keep it cool. We close all drapes and turn on ceiling fans and floor fans plus run the fan when the air conditioner itself is not running, but the temperature still hovers around 78ºF or more during the afternoon in the house.
I have had two different air conditioning people to the house and both of them said the size of my air conditioner was correct. One of them said I couldn’t put in a larger system, since it would require enlarging all the ducts in the house. We normally have low humidity here, but for the past few years the temperature has averaged in the mid-90s for highs during the summer. I am at the point where I just don’t know what to do to keep it cool enough for my wife and sincerely hope you might have a suggestion or two. Please let me know what to do.
Colorado Springs, Colorado
House Doctor John Proctor replies:
It is rare for an air conditioner to be undersized, but it is possible. The real way to know is to have an ACCA Manual J calculation done for your home, room by room and zone by zone. Did any of the contractors do that?
Seventy-eight degrees is not an unusually high indoor temperature. Most designs aim at 75ºF. It may be that your comfort level requires lower temperatures than many people. Or are the temperatures in the rooms in question actually higher than 78ºF?
You have pinpointed one significant afternoon heat source—the west-facing windows. You have also done the most logical thing—closed the drapes. Running the floor fans and ceiling fans may make you feel cooler (they increase evaporation off your skin), but these fans actually add heat, raising the temperature in the house. Try turning off the ceiling fans first.
Running the A/C fan all the time is a bad idea. It brings duct leakage into play, which increases the temperature in the house. —Not to mention the fact that all that fan energy also winds up as heat in the house.
The contractor is probably right about enlarging your ducts, since most duct systems are too small to begin with.
You wrote that you don’t know whether the air conditioner is actually delivering its capacity. In general it will not be, for one or more of three reasons. These are:
• incorrect charge;
• low air flow; or
• leaky ducts.
Here are some suggestions (in chronological order):
1. Stop running the A/C fan all the time.
2. Find someone in Colorado Springs who can test the duct leakage. There are many companies in the area that have Duct Blasters.
3. Find someone who will check refrigerant charge using superheat or subcooling.
4. Find someone who will measure the supply and return wet and dry bulb temperatures, and air flow through the unit and compare the readings to what they should be for the test conditions.
If none of these suggestions solves the problem, consider replacing the west-facing glass with low-e2 insulated glass units (I assume the current windows are already double pane), and revising the duct design for the upper story to supply more air to the upper-story west rooms.
Did I give you enough to do?
Help! Can you tell me how I can determine if my A-coil is clogged? What should be the maximum pressure drop across the coil? I live in a single-family, single-level three-bedroom house (plus a finished basement). To check for leaky ducts: What should be the air pressure between open and closed vents? How cold should the air be when it leaves the vent? Is there any literature available for a common person, but good mechanic, with basic knowledge of heating and air conditioning?
I live in a rural area in Missouri and have little commercial help. Any help will be appreciated greatly.
John Proctor responds:
The pressure drop across your A-coil should be less than 0.35 inches water column (WC) (measured between the A-coil entrance and the A-coil exit). The best test for leaky ducts is with the Duct Blaster (see www.energyconservatory.com). Here are two other possibilities:
• Check with your hand for register flow—low flow means a leak is possible.
• Borrow a window fan, put it in a window, and turn it on, forcing air into the home. Go to the registers and see which ones have air flowing into them—those are the ones closest to the leaks.
The difference in temperature between the air leaving the air conditioner and the air entering the air conditioner should be as noted in “Checking an Installation” (HE Jan/Feb ’02, p. 10).
The difference in temperature between the air leaving the air conditioner and the air leaving the ducts should be less than 1ºF (this will change depending on the temperature of the space the ducts run through). The difference in temperature between the air entering the return grille and the air entering the air conditioner should also be less than 1ºF (this too will change with the temperature of the air in the space the return ducts run through). The temperature differences are best tested on a very hot day.
In your article titled “Tankless Option Improving” (July/August ’05, p. 18) you listed several tankless models. In your listings you have Rinnai models 2402 and 2424 respectively. Both units are outdated and have been replaced by the model 2532 Continuum. The minimum firing rate is now 15,000 BTU and it has the same 180,000 BTU max input at 0.82 efficiency factor for indoor models and 199,000 for the outdoor units. Also the units are 0.87 efficiency factor on propane.
Northwestern Regional Manager
Water Heater Division
Rinnai America Corporation
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