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NATURAL HEATING AND COOLING

The first step in design for natural heating and cooling (sometimes calledpassive solar design) is improving the thermal performance of a building.Improving the energy efficiency of a building beyond the standard level isremarkably easy. In most areas it is reasonable to expect at least a doubling inthe energy efficiency with only a modest increase in cost. The following stepsshould be included:

A) orientation,B) insulation, C) weatherization,D) shading and E) landscaping.

Other Information: PassiveSpace Conditioning, SixRules for Low Cost Natural Heating, SixRules for Natural Cooling, Simple PassiveHomes, Water Wall House, TrombeWall House, Solar Greenhouse, RoofPond.


A.Orientation

Good orientationis essential for an energy efficient structure. The effects of bad orientationcan be remedied to some extent - but doing so can be expensive. The bestorientation is for a building to be longer east-west that it is north-south,with a major yard to the south, and mostof the windows facing south and a few facing north, east, or west. Thisorientation will maximize solar heating in winter and minimize summeroverheating by making best use of the seasonal difference in sun path. This waswell understood in Ancient Greece and Rome where houses were solar oriented andeven communities were laid out for good solar access. In the later days of Romelegal action could be brought to maintain solar access to keep a home warm inwinter.

     A structure with less than ideal shape can work well if some glazing ison the south side and the other windows are properly designed.

B.Insulation

The second stepin building or remodeling for energy efficiency is reducing unwanted conductiveheat loss (or gain). Insulation is the key - not only for the walls and ceiling,but also for the foundation or slab perimeter, windows, doors, and the peopleinside. Most homes are woefully under-insulated. Typical wall insulation levelsare still R-13 to R-19 in many areas of the country, but they should be atminimum R-30 and R-50+ is much better. Straw bale buildings offer R-50 walls atthe same cost as conventional buildings with R-19. Ceiling or roof insulationshould also be R-50+ in most areas. Double pane windows are a minimum and highperformance windows or double pane plus storm windows are usually costeffective. Insulated drapes and shutters are very effective on windows and skylights.

C.Weatherization

Infiltrationlosses are as important as conductive losses and careful weatherizing isnecessary. This includes both the obvious problems of weather-stripping doorsand windows and also the more general problems of caulking and sealing buildingjoints, access holes, and other areas where unwanted infiltration occurs.Infiltration may easily account for half of the heat loss in a well insulatedbut poorly weatherized house. The infiltration rate on a typical house is around1.5 air changes/hour, but can go significantly higher if the wind is blowing.With careful attention to detail the air exchange can be reduced to 0.2 airchanges/hour. The goal is to have controlled ventilation so the air comes inwhen and where you want it and is fresh and healthy. A super-insulated solarhouse will perform so well it is often possible to have several windows slightlyopen almost all winter. In very cold areas an air-to-air heat exchanger isdesirable for ventilation during the coldest periods. The heat exchanger warmsthe incoming fresh air with warm stale outgoing air.

D.Shading

Shading andsolar control is critical to prevent overheating in the summer. The importanceof shading is best illustrated with an example. In the Central Valley nearSacramento, California just 55 square feet of west facing glass will add as muchas 55,000 BTU to a house on a summer afternoon. A substantial air conditionerwill be required to offset this heat gain. Running an air conditioner at thispeak period of electrical demand may require almost 2 kw of added generationcapacity to be built, which will cost the utility $2,000+. The homeowner alsohas to pay for the air conditioner and the energy for its operation over thelife of the house, which may also exceed $2,000+. This entire cost could beavoided completely by proper orientation of the house, or largely avoided by useof an exterior shade costing less than $100.

     Shading or solar control is relatively easy if the house is orientedproperly. Overhangs and wing walls can shade the south windows. The otherwindows can be shaded with awnings, wing walls, wide overhangs, exterior shades,shade screens, arbors or trees.

E.Landscaping

Very substantialsavings in energy use for heating or cooling may be realized by altering theenvironment the house sits in. Landscaping can provide shading in the summer andwind protection in the winter. Landscaping can also channel cooling breezes insummer. The most important areas for control are the east and west windows andwalls.

PassiveSpace Conditioning

After improvingthe energy efficiency of a building, we can apply the following principles ofsimple solar design to make it a naturally heated and cooled house. These simplesolar systems are very effective for space heating.

Passive solarheating systems differ widely in configuration, performance and cost, but haveseveral features in common. These include: windows or glazing to admit the sun'senergy, glazing control (insulated drapes or shutters) to reduce unwanted heatloss or heat gain and thermal mass to store the sun's energy.

 

SixRules for Low Cost Natural Heating:

1. Make sure the building is verywell insulated and weathertight.

2.Make sure the structure is oriented properly, with several windows on the southside. A rectangular shape that is wider east-west than north-south is best.

3.Use the minimum amount of south window area needed for heating (often only 5-8%of floor area). Most early solar homes had too many windows and not enoughinsulation.

4.Buy the best windows you can afford and make insulated shades or shutters forwindows simple, reliable, effective, and convenient to use.

5.Use the simplest, smallest, and most economical method of providing neededthermal mass. This will often be doubled sheet rock in south rooms, thickerplaster, concrete or tile floors and water tanks.

6. Consider cooling demand as well and integrate design to achieve lowestcost heating and cooling.

 

SixRules for Natural Cooling

1. Make sure the building is oriented properly with most windows on southand north, few on east and west.

2. Provide shading for all windows in summer (awnings, overhangs, etc.).Use landscaping to improve cooling.

3. Use light roof colors and lightwall colors.

4. Choose and place windows and vents for good ventilation and convectivecooling. Undercut doors or use open plans to provide good ventilation. Usepaddle fans for air circulation, use night ventilation (consider a whole housefan) if night air temperatures are low.

5. Use thermal mass (water tanks, doubled sheet rock, plaster, rock, tileor concrete) to store nighttime coolth for use during the day.

6. Consider heating demand as well and integrate design to achieve lowestpossible cost.

Following these rules candramatically improve comfort and security. A well designed naturally heated andcooled house will work even when the power is down. It will also reduce energydemand for heating and cooling 50% or more. In many cases energy demand can bereduced 90%.

Five of the best natural solarheating and cooling systems are the simple passive solar house, water wallhouse, trombe wall house, solar greenhouse and the roof pond house.  

SimplePassive House

Every standard frame house can be apassive solar house if It is properly designed and exposed to the sun. To workwell it should be oriented so a major wall and many windows face south. Addedinsulation and improved (double pane+) windows are desirable. Slab edgeinsulation is needed. Exposing the slab floor will increase thermal storage. Usetiles, integral color, linoleum, or parquet (not carpet) to increase heattransfer. East and west windows must be fully shaded in hot areas. South windowscan be shaded with a wider overhang or vine covered arbor. Interior insulateddrapes or shutters are helpful.

 

WaterWall House

Adding more thermal mass to asimple passive house can greatly improve its performance for both heating andcooling. A custom steel water tank is a good way to provide this thermal massbecause the water is much more effective at collecting and reradiating heat thanconcrete or plaster. The water tank stores the sun's energy for nighttimeheating in the winter and the night's coolness for use on hot summer days. Waterwall homes are very comfortable and economical. Good exposure of the tanks tothe sun is desirable and they are usually placed directly in front of southwindows, perhaps to counter height or bench height with cushions on top. Tankthickness less than one foot is optimal in most temperate climates.  

TrombeWall House

Concrete, stones or masonry canalso be used to store the sun's energy. Because they are less than one-third aseffective as water at storing energy much more mass is needed. The thickness ofthe mass walls is usually kept to a foot or less. A typical installation willuse the concrete mass wall on most of the south side of the house with windowsoutside the entire wall. This type of solar system has been used in very coldareas with considerable success.Venting and shading are critical to prevent unwanted heat gain in the summer.

SolarGreenhouse

The solar greenhouse or solarium iswell suited for colder areas where heating is more important than cooling. Thesun's energy is captured in the greenhouse and then vented into the house. Inmost cases a solar greenhouse should have internal thermal mass to reducetemperature swings. The space should also be very well ventilated and shaded inthe summer to prevent overheating.

RoofPond

Thermal storage can also beprovided in a roof pond over the house. This type of house allows a moreflexible interior plan and is the best option where cooling is the predominantrequirement. The water must be placed on a thermally conductive support (usuallymetal decking) and exposed to the sun during the winter days and the cool nightsky on summer nights. In areas where winter heating is needed insulated lidsmust be used at night, the most effective pivot upward on hydraulic rams. Incooling only areas lids may be replaced with full shading, and ponds may be opento add evaporative cooling. Alternatively the water can be moved to an insulatedspace and pumped into the pond as needed.

With simple natural heating andcooling techniques the comfort of homes can be improved in any climate. In manyareas these can be built a cost equal to conventional homes that requireexpensive air conditioning and heating systems. Natural heating and cooling willwork in the hot deserts of the southwest to the icy winters of northernMinnesota.

Because peak power demand in mostareas of the country is driven by heating (January) and cooling (August) thetrue savings are much greater because these naturally heated and cooled homesrequire little or no added generating capacity. The energy and financial savingsover the lifetime of these naturally heated and cooled homes are dramatic andimportant for America's future.

Written by: Sustainable Energy


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