BUILDING GREEN - Step 5. Choose the Right Mechanical Systems

BUILDING GREEN - Step 5. Choose the Right Mechanical Systems.
Modern heating, cooling, and ventilation systems, lighting, and appliances play a major role in providing us with comfort and convenience, good health and safety. If you understand a few basics about each of them, you’ll be able to get all these benefits for a reasonable price. A. Mechanical systems: heating, cooling and ventilation Feeling comfortable depends on a complicated mix of factors—not just the temperature of the air, but also the relative humidity, the rate of air movement, and the temperature of the materials around us. Examples: A hot day in Santa Fe probably won’t feel as bad to you as an equally hot day in Houston, because Houston is humid as well as hot. If you sit under a ceiling fan on a hot day, you may not need any air conditioning. If you sleep on an unheated waterbed, you may feel it drawing the heat out of your body. If you go downtown on a hot summer day, you’ll feel heat radiating toward you from all the concrete and asphalt. By incorporating many passive design features, such as super insulation, careful sizing and placement of windows, and air-lock vestibules, this house in Maine needs so little electricity, the need can be met entirely with active solar equipment. By far the most cost-effective way to feel comfortable in a building is to control your environmental conditions by passive means: finding a site that protects you from the worst elements of your region, and designing your building and choosing materials that do the same (Step 3 and Step 4). But passive methods won’t make you perfectly comfortable all the time in most parts of the country. For that, you’ll need an
active heating, cooling, and ventilation system.

Note: much of the following discussion applies only to a forced-air system—one in which heated or cooled air is blown by fans through a duct system, which distributes the air around the building. We’re emphasizing forced air systems here because central cooling requires them and they are still the most common system for heating, too. You may find a different kind of system better suited to your needs. To get comfort, safety, and affordability from your system, consider efficiency, humidity control, air movement, air quality, and system type.

1. Efficiency
Whether your system will be efficient depends on the following:
a. Efficient equipment
Your mechanical system costs you money every minute it runs. In a cold climate, choose equipment with the highest heating efficiency rating you can afford to purchase. If you get air conditioning too, but aren’t likely to use it much, don’t spend a lot to get high cooling efficiency. In a hot
climate do just the reverse.
b. Correctly sized equipment
Equipment size must be based on the actual amount of cooling and heating a building needs. Need is based on the climate, size, design, and construction of a building—factors such as the amount of window area and the direction it faces, the kind of windows and how they are shaded, the
amount of insulation, etc. If the equipment is too small, it can’t heat or cool adequately. But in most
homes, the equipment is too big to work right. Because an oversized unit reaches the temperature on the thermostat very quickly, it doesn’t run long enough at one time to reach the efficiency it was designed for. It’s like a car always driven in town and never on the highway: operating expenses are
higher and it wears out faster. In a hot, humid climate, you cheat yourself even more with an oversized unit. To be comfortable in these conditions, you need the cooling system to dry out the air, as well as cool it. The system can only respond to the thermostat, however, and the thermostat only reads air temperature (not humidity), so it shuts off before it can dehumidify properly. As a result, you’ll feel clammy, and maybe sick as well from the mold thriving in the warm, moist air. In short, equipment that’s too big for the job costs more to purchase, more to operate, reduces comfort, and compromises health. In most homes, mechanical equipment is too big to work right.
c. Effective placement
The best location for equipment and ductwork is inside the insulated space, so conditioned air is less affected by outside conditions. If a house has an insulated basement, that’s a good location. In the south, however, houses rarely have basements, so systems are usually put in attics. Since an attic may get up to 160 degrees on a summer day, that’s the worst possible place to run ducts filled with cold air. (Ducts are insulated, but only minimally.) Note: The attic wouldn’t be such a bad location if the insulation were installed just under the roof, instead of its usual place on the floor of the attic. Then the ductwork would be inside the insulated space.
d. Effective design and installation
The extra money you pay for high-efficiency equipment will be wasted if the system is poorly installed. For example, if the installer puts 90-degree turns in the ducts that weren’t allowed for in the design, the extra friction caused by air swirling around the sharp bend will prevent the needed amount of air from getting to the rooms. If the ducts leak (and they always do), conditioned air
seeps out of the duct, or unconditioned air gets sucked in. Most leaks cannot be seen. They can only be found by testing. Testing is not standard practice, so you must ask for it. Leaks must be sealed with a material, such as latex mastic, that won’t come off or disintegrate over time.

2. Humidity Control
At moderate temperatures, if relative humidity drops below 20%, viruses proliferate; if it rises above 60%, molds grow. Mold is the leading cause of occupant health problems and rotting building materials. Mold didn’t used to be such a problem in old leaky buildings, but now that we build tightly to save energy, it is a serious problem (one of those unintended consequences). How can you control relative humidity inside your home? In the north, relative humidity tends to drop uncomfortably low in winter when the heat is on, so you may need a humidification system. In humid areas, you need cooling equipment with an extra high capacity for dehumidification. Reminder: be sure the cooling equipment is sized small enough to run a lot, since it can only dehumidfy when it’s running. A smaller unit is cheaper to buy and cheaper to run. If you live where there are lots of humid days in spring and fall when you don’t need heating or cooling, consider installing a separate dehumidification system. This is not yet very common and is often seen as an extravagance, but as more people understand the effect of moisture on both comfort and health, they will consider such a system to be a standard part of good building.

Note: In extra humid rooms of the house, such as baths, laundry and kitchen, be sure to install vent fans that exhaust air to the outside. You can connect them to a timer, or better yet, a humidity-sensor, so they’ll turn off automatically. Also, the quieter the fan, the more likely you are to use it. The average new house loses over a quarter of its heated or cooled air due to leaky ducts. Imagine what effect that has on your utility bill. How do you know what the relative humidity is inside your house? An inexpensive humidistat (under $25) from your local electronics store will tell you. You’ll soon notice how both temperature and relative humidity relate to how comfortable you feel.

3. Air Movement
It’s important for a heating and cooling system to move enough air to and from every room (both supply and return) to function properly and provide comfort. The location of supply and return registers is also critical to good airflow. You’ll have to rely on a mechanical engineer or contractor to plan this, but let him or her know this is important to you.

4. Air quality and safety
When you turn on your forced-air system, huge changes in air pressure occur. Dangerous fumes from a gas furnace or gas water heater (such as carbon monoxide) may get sucked into the living space instead of exhausting out of the house through the vent pipes. This is called backdrafting. For safety’s sake, choose a sealed-combustion unit that gets oxygen for combustion from outside the house instead of robbing it from the air you breathe. A good filter improves air quality and protects your equipment (many filters do neither). Filter efficiency ratings are often wildly misleading. For example, a claim of 95% efficiency may only mean it’s good at filtering out marbles. A pleated-media filter does a good job for the least money.

5. Type of system
The best type of system for your home will vary from one part of the country to another, for all the usual reasons—conditions, availability, expertise in your community, budget, and so forth. For example, radiant heating may be a good choice in a cold climate, but it’s usually not cost-effective in hot climates. Air conditioning requires ductwork for the distribution of cold air, so you’ll probably want to use the ducts for heating too, instead of spending even more for a totally separate heating system. Evaporative cooling that gets cooling from the evaporation of water is efficient, but works well only in a dry climate. A geo-thermal heat pump, that uses the earth or water to heat and cool, is efficient, quiet, and long-lived, but installation is so costly in some parts of the country, the purchase price may outweigh the benefits for most people. Ceiling fans are a great way to increase comfort in hot weather. They cost about the same to run as a 100-watt light bulb. Note that fans don’t actually make the air cooler, but they do make you feel cooler when you’re in the path of moving air.

B. Lighting
If you compare a well-lighted building with a poorly lighted one, you’ll know that good lighting is not a luxury. It’s necessary for people to be productive, healthy, secure and safe. It’s also important for its psychological effects—the way it can make space cheerful, welcoming, cozy, interesting, romantic, or dramatic. Let’s look at how we can get better light in buildings—whether from daylight or electric lighting.

1. Daylight
There’s nothing like light from the sun for high quality and efficient light, but bringing it inside a building can be tricky. Be sure to consider this at Step 3, when you decide on size and placement of windows and overhangs, and at Step 4, when you choose the window units. To get the maximum benefit from daylight, be sure your designer gets light as deep into the living space as possible. Windows high on a wall are especially effective for doing this with a minimum of annoying glare. You want light to hit as many surfaces as possible and reflect back on other surfaces. Light-colored paint increases reflection. Be cautious about the use of skylights because they may allow too much heat in.

2. Electric Lighting
When there’s not enough daylight, we must depend on electric lighting. Luckily, there is a wide selection of fixtures and bulbs to choose from, depending on what you need light for, the amount you need, the efficiency you want, the way you want colors to look, whether you need focused or diffused light, and where you intend to place light fixtures. High vertical windows with a properly-sized overhang let in a lot of light without a lot of glare or heat (unlike skylights).

a. Purpose of the light
Your lighting choices should depend on what you are trying to accomplish with lighting. Do you need general lighting to get around easily and safely; indirect lighting to bounce off surfaces and keep spaces from looking gloomy; intense, highly focused and totally glare-free light for tasks such as reading or sewing; accent lighting to highlight a painting or architectural feature; or decorative lighting, such as a chandelier?

b. Type of light
Choose the best kind of light for your purpose. For residential use, you will probably stick to standard incandescent lighting for creating a warm, cozy atmosphere; halogen incandescent when you need a very intense or focused light for reading or highlighting an object; or fluorescent for most other uses, since it’s very efficient, long lasting, and doesn’t produce a lot of heat. You might be surprised to learn that fluorescent lighting is now available with electronic ballasts that don’t flicker or hum, and light that is warm and flattering in color. You may have to go to a commercial lighting supplier to find the fixtures and bulbs you want. Over its lifetime, an 18-watt fluorescent light will save about 570 kilowatt hours of electricity (which saves over 1,300 pounds of carbon dioxide emissions) compared to a 75-watt incandescent bulb (which gives about the same amount of light).

c. Amount of light
Install the amount of light needed for your purpose. For example, you might think you need a lot of light to see outside at night, but actually you need very little. A little seems like a lot because at night the contrast is so great. A major reason not to use more than you need is the fact that lighting produces a lot of heat. An incandescent bulb turns only 7% of the electricity it uses to light—the other 93% turns into heat. In a hot climate that’s a big drawback (and even in a cold climate, not a very efficient way to heat your house). In a commercial building, the amount of cooling needed to counteract the heat from lighting may be greater than the amount needed to overcome heat from the climate.

d. Fixture type and placement
Choose fixtures that throw light where you need it, and place light fixtures where they will do their job best, without causing annoying glare. Your home designer may be able to advise you about this, or you may want to add a professional lighting designer to your team. You can also seek advice from a commercial lighting supplier. Note: Recessed can fixtures are very popular, but unless they are the sealed, energy-efficient type, they are an energy disaster. The unsealed kind produces
so much heat, it can’t be safely insulated, and is like a hole in the ceiling. Also, recessed cans are frequently placed and finished out with useless and glaring down-lighting, when they could be used for effective and attractive wall lighting instead.

C. Appliances
Americans love the convenience of appliances. In spite of the increased energy
efficiency of new appliances, households are using more energy than ever, however,
because they are using more appliances, especially computers. That’s all the more
reason to look for efficiency of both energy and water when choosing appliances.

1. Look for energy-efficiency labels, such as the EnergyGuide or Energy Star.
It’s easy to find and understand the bright yellow EnergyGuide label on appliances such as refrigerators, dishwashers, and stoves. Be sure to compare the actual energy use of a given appliance with other sizes and models. For example, a larger refrigerator could actually have a lower energy use than a smaller one. When purchasing appliances such as computers, look for the Energy Star label. Check the U.S. Department of Energy web site at www.energystar.gov to find out the energy efficiency of the models you are considering. The EnergyGuide label shows you how a particular model of appliance compares in energy efficiency with other models of a similar size and type. Look for the Energy Star label when purchasing appliances.

Life-Cycle Costs for 13-Year Operation of Different Types of Water Heaters

WATER HEATER TYPE EFFICIENCY COST* YEARLY ENERGY COST** LIFE (YEARS) COST OVER 13 YEARS***

Conventional gas storage 55% $425 $163 13 $2,544

High-efficiency gas storage 62% $500 $145 13 $2,385

Oil-fired free standing 55% $1,100 $228 8 $4,751

Conventional electric storage 90% $425 $390 13 $5,495

High-efficiency electric storage 94% $500 $374 13 $5,362

Demand gas 70% $650 $140 20 $2,243

Demand electric (2 units) 100% $600 $400 20 $5,590

Electric heat pump 220% $1,200 $160 13 $3,280

Indirect water heater with efficient oil or gas boiler
75% $700 $150 30 $2,253

Solar with electric back-up na $2,500 $125 20 $3250

* Approximate. Includes installation.
** Energy costs based on hot water needs for typical family of four and energy costs of $.08/kWh for electricity, $.60/therm for gas, $1.00/gallon for oil
*** Future operation costs are neither discounted nor adjusted for inflation.
Source: American Council for an Energy-Efficient Economy.

2. Estimate the life-cycle cost.
What is the true cost of your choice over time, not just the purchase price? Compare the purchase price column with the total cost column on the right. Any surprises? Notice that the electric water heaters are extremely efficient, but they are the most costly in the long run. How come? For an excellent guide to the energy use of appliances, see The Consumer Guide to Home Energy Savings listed below.