Chapter 7.Passive Solar

Contents

7.1 Introduction7.2 Types of Passive Solar Systems7.3 Advantages and Disadvantages7.4 General Design Principles7.5 Design Information for Direct System7.6 Design Information for Sunspace7.7 Movable Insulation7.8 Shading Devices7.9 Summer Cooling in Passive Solar Houses7.10 Conclusions (Ten Rules of Thumb)

7.1 INTRODUCTION

• “Passive Solar” refers to a system that collect, stores, and redistributes solarenergy without the use of fans, pumps, or complex controllers.

• It functions by relying on the integrated approach to building design, where thebasic building elements, such as windows, walls, and floors, have as manydifferent functions as possible.

• For example, the walls not only hold up the roof and keep out the weather butalso act as heat-storage and heat-radiating elements.

• Every passive solar heating system has at least two elements:

1) Collector: consisting of south-facing glazing2) Energy storage: consisting of thermal mass, such as rock or water.

• Passive solar is part of the rational design accomplished through the three-tierdesign approach.

• A passive solar building can provide 60 to 80 percent of the required heating intemperate climatic regions.

7.2 TYPES OF PASSIVE SOLAR SYSTEMS

• Depending on the relationship of the solar collector and the energy-storage, thereare three main types of passive solar systems.

1) Direct gain system2) Indirect gain system3) Isolated gain system

1) Direct Gain System

• This is the simplest approach to passive solar heating.

• The actual living space is directly heated by solar radiation.

• Large south-facing windows are required.

• Thermal mass of about 1/2 - 2/3 of total surface area is required to store heat.

2) Indirect Gain System

• The thermal storage mass is located between the sun and the space.

• The thermal storages include:

(1) Trombe walls: masonry or water thermal storage wall

(2) sunspace

(3) roof ponds

(1) Trombe Walls

• The Trombe wall was named after professor Felix Trombe, who developed thistechnique in France in 1966.

• The thermal mass consists of a wall just inside the south-facing glazing.

(2) Sunspace

• A sunspace is a room designed to collect heat for the main part of a building, aswell as to serve as secondary living area.

• Sunspaces are one the most popular passive systems, not only because of theirheating efficiency, but also because of the amenities that they offer. Most peoplefind the semi-outdoor aspect of sunspaces very attractive. Almost everyone findsit pleasurable to be in a warm, sunny space on a cold winter day.

• One of the best-known passive solar houses with sunspace is “Balcomb House”located in Santa Fe, New Mexico.

(3) Roof Ponds

3) Isolated Gain System

• Solar collector and thermal storage are isolated from the living spaces.• Flat plate solar collectors utilize the natural convective loop to produce hot

water or hot air.

• Economic advantages:- large savings of energy and heating

- little or no additional cost in the original design and construction

• Architectural advantages:- simplicity of its design

- simple operation and maintenance (no mechanical equipment)

• Comfort/health advantages:- higher indoor surface temperature (MRT) and lower air temperature

enhance the sensation of comfort and health- higher floor temperature = small floor-to-ceiling temperature gradient

7.3 ADVANTAGES AND DISADVANTAGES

• Disadvantage and Solutions:

- large heat storage capacity = slow response- temperature fluctuations in incorrectly designed system

- solutions: operable windows

shading devices

back-up heating system

1) Building Location

• Allow solar access between the hours of 9:00 a.m. and 3:00 p.m.(approximately 90 % of the solar energy received)

7.4 GENERAL DESIGN PRINCIPLES

• Place the building in the northern portion of the site.

H

D <= 2.5 H

2) Building Shape and Room Depth

• Elongate the building along the east-west axis.• Room depth should not exceed the 2.5 times the floor-to-window height.

3) North Side

• Shape the building so that its north side slopes toward the ground.

• Use a light-colored wall to the north of the building to reflect sunlight tooutdoor spaces.

4) Location of Indoor Spaces

• Place critical rooms to the southeast, south and southwest location.• Place closets, stairs, and corridors to the north location (thermal buffer).• The west side will be slightly warmer than the east side because of the

combination of solar radiation and higher afternoon air temperature.

5) Protected Entrance• make the main entrance to the building a small enclosed space (double

entry or air lock between the building and exterior)• orient the entrance away from the prevailing winter wind (east or south side

is recommended)• provide a windbreak to reduce the wind velocity against the entrance

(recessed entrance or wing walls)

6) Window Location• Locate major window openings to the southeast, south, and southwest.

• On the east, west and especially north side of the building, keep windowareas small and use double glass.

7.5 DESIGN INFORMATION FOR DIRECT GAIN SYSTEM

1) Solar collector windows (south-facing windows)• cold climate: 19 - 38 % of floor area

• temperate climate: 11- 25 % of floor area

2) Clerestories and Skylights

• Clerestories or skylights are effective solar collector for a building siteelongated along the south-north direction.

3) Masonry Heat Storage• minimum thickness = 10 cm• a dark color for masonry floors• any color for masonry walls• paint all lightweight construction a light color• avoid direct sunlight on dark-color masonry surfaces for long periods of

time (use diffusing glass)• do not use wall-to-wall carpeting over masonry floors

4) Interior Water Wall• size and surface color affect the temperature fluctuation in a space over the day• size = 1 m3 of water for each 1 m2 of solar collector windows• surface color = dark color (black)

7.6 DESIGN INFORMATION FOR SUNSPACE

1) Size of South-Facing Double-Glazed Greenhouse

• Cold climate: 65 - 150 % of building floor area• Temperate climate: 33 - 90 % of building floor area

2) Sunspace Connections

7.7 MOVABLE INSULATION

• to keep heat inside at night

7.8 SHADING DEVICES

• The lengths of a horizontal overhangs for south-facing windows can bedesigned by considering solar profile angle, wall-solar azimuth angle, andwindow height.

WinterSummer

Manually operated exterior shading device

7.9 SUMMER COOLING IN PASSIVE SOLAR HOUSES

• make the roof a light color or reflective material

1) hot-dry summer (Convective Ventilation)• open the building at night to ventilate and cool interior thermal mass• provide large openings of equal sizes on opposite sides• close the building during the daytime to keep the heat out

2) hot-humid summer (Comfort Ventilation)• open the building during the day and evening for the prevailing summer

breezes• make the area of the outlets slightly larger than the inlets to obtain higher

wind velocity

7.10 CONCLUSION (TEN RULES OF THUMB)

1) Locate building to the north part of site.

2) Elongate the building along the east-west axis.

3) Maximum room depth is 2.5 times the height of window head from the floor.

4) Locate major living areas to southeast, south and southwest and buffer space at northpart.

5) Provide protected entrance (double door or windbreak) against cold winter wind.

6) Minimum thickness of masonry thermal storage material is 10 cm.

7) Size the south-facing window area considering climate (minimum 20 % of floor area).

8) Use proper surface colors; dark color for masonry floor, any color for masonry wall,and light colors for furniture.

9) Install movable window insulation for nighttime.

10) Install proper shading devices for summer.