9.6: Natural Cooling
- Page ID
- 47210
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Energy Savings by Naturally Cooling Your Home
Keeping cool indoors when it is hot outdoors is a problem. The sun beating down on the homes causes indoor temperatures to rise to uncomfortable levels. Air conditioning provides some relief. But the initial costs of installing an air conditioner and the electricity costs to run it can be high. In addition, conventional air conditioners use refrigerants made of chlorine compounds, suspected contributors to the depletion of the ozone layer and global warming. But there are alternatives to air conditioning.
An alternative way to maintain a cool house or reduce air-conditioning use is natural (or passive) cooling. Passive cooling uses non-mechanical methods to maintain a comfortable indoor temperature.
Specific methods to prevent heat gain include:
- reflecting heat (i.e., sunlight) away from your house;
- blocking the heat;
- removing built-up heat
- reducing or eliminating heat-generating sources in your home.
Reflecting Heat Away
Dull, dark-colored home exteriors absorb 70 to 90 percent of the radiant energy from the sun that strikes the home's surfaces. Some of this absorbed energy is then transferred into a home by way of conduction, resulting in heat gain. In contrast, light-colored surfaces effectively reflect most of the heat away from a home.
Blocking the Heat
Two excellent methods to block heat are insulation and shading.
Insulation helps keep your home comfortable and saves money on mechanical cooling systems such as air conditioners and electric fans.
- Shading devices block the sun's rays, absorb or reflect the solar heat, and reduce indoor temperatures by as much as 20° F. Shading can be provided by trees and other vegetation or exterior or interior shades.
- Exterior shades are generally more effective than interior shades at controlling heat gain because they block sunlight before it enters windows. Exterior shading devices include awnings, louvers, shutters, rolling shutters and shades, and solar screens.
- When deciding which devices to use and where to use them, consider whether you are willing to open and close them daily or just put them up for the hottest season. You also want to know how they will affect ventilation.
Removing Built-Up Heat
Nothing feels better on a hot day than a cool breeze. Encouraging cool air to enter your house forces warm air out, keeping your house comfortably cool. However, this strategy only works when the inside temperature is higher than the outside temperature.
Natural ventilation maintains indoor temperatures close to outdoor temperatures and helps remove heat from your home. But only ventilate during the coolest parts of the day or night, and seal off your house from the hot sun and air during the hottest parts of the day.
The climate you live in determines the best ventilation strategy, some of which are listed in Table 9.6.1.
Table 9.6.1. Cooling strategies for various climates
Climate | Strategy |
---|---|
Cool nights, very hot days | Let night air cool the house. A well-insulated house will gain only 1° F (0.6° C) per hour if the outside temperature is 85° to 90° F (29° to 32° C). By the time the interior heats up, the outside air should be cooler and can be allowed indoors. |
Daytime breezes | Open windows on the side from where the breeze is coming and on the opposite side of the house. Keep interior doors open to encourage whole-house ventilation. If your location lacks consistent breezes, create them by opening windows at the lowest and highest points in your house. This natural "thermosiphoning," or "chimney," effect can be taken a step further by adding a clerestory or a vented skylight. |
Hot and humid, temperature doesn't change much between day and night | Ventilate when humidity is not excessive. Ventilating your attic greatly reduces the amount of accumulated heat, which eventually works its way into the main part of your house. Ventilated attics are about 30° F (16° C) cooler than unventilated attics. Properly sized and placed louvers and roof vents help prevent moisture buildup and overheating in your attic. |
Reducing Heat-Generating Sources
Often-overlooked sources of interior heat gain are lights and household appliances, such as ovens, dishwashers, and dryers. Table 9.6.2 lists more examples.
Table 9.6.2. Reducing heat-generating sources
Heat generating light or appliance | Reducing heat |
---|---|
Incandescent lamps | Use only when necessary and take advantage of daylight to illuminate house. Also consider switching to fluorescent lamps, which use 75% less energy than incandescent lamps and emit 90% less heat for the same amount of light. |
Kitchen appliances | Use in the morning or late evening when extra heat can be tolerated. Consider cooking on an outside grill or using the microwave oven, which does not generate as much heat and uses less energy than a gas or electric range. |
Laundry appliances | Seal off laundry room and water heater from rest of room. Purchase new energy-efficient appliances that generate less heat and use less energy. Look for the Energy Guide label indicating the annual estimated cost for operating the appliance or a standardized efficiency ratio, and use this information to select the most efficient model for your needs. |