Thermal Analysis and Design of Passive Solar Buildings

AK Athienitis, M. Santamouris

• Publisher: Routledge
• Year: 2013
• eBook ISBN: 9781134274215
• Edition: 1
• Topic: Architecture
• Subtopic: Architecture General

Passive solar design techniques are becoming increasingly important in building design. This design reference book takes the building engineer or physicist step-by-step through the thermal analysis and design of passive solar buildings. In particular it emphasises two important topics: the maximum utilization of available solar energy and thermal storage, and the sizing of an appropriate auxiliary heating/cooling system in conjunction with good thermal control.

Thermal Analysis and Design of Passive Solar Buildings is an important contribution towards the optimization of buildings as systems that act as natural filters between the indoor and outdoor environments, while maximizing the utilization of solar energy. As such it will be an essential source of information to engineers, architects, HVAC engineers and building physicists.

Chapter 1
Introduction and basic concepts

1.1 Passive solar design principles - an introduction

Solar radiation is the most abundant renewable energy source, without which life on earth would be impossible. It is the driving energy of our ecosystem and of the precipitation cycle. Passive solar design principles have been known to our ancestors since antiquity; for example ancient Romans oriented house openings towards the south so as to be warm in the winter and reduce solar gains in the summer. They also built massive dwellings that reduced room temperature fluctuations. In some countries of the Mediterranean the living room is known as the ‘solar room’, and in traditional architecture it connects into a south-facing courtyard.

The term ‘passive solar building’ is a qualitative term describing a building that significantly utilizes solar gains to reduce heating and possibly cooling energy consumption based on natural energy flows - radiation, conduction and natural convection; forced convection based on mechanical means such as pumps and fans is not expected to play a major role in the heat transfer processes. The term ‘passive building’ is often employed to emphasize utilization of passive energy flows both in heating and cooling.

Passive solar heating systems are generally separated into two broad categories, direct gain and indirect gain (see Section 1.7). When indirect passive systems are insulated from the heated space they are sometimes referred to as isolated.

Passive solar design techniques address the following basic requirements and principles:

• Transmission and/or absorption of the maximum possible quantity of solar radiation during winter so as to minimize or reduce to zero the heating energy consumption.
• Utilization of received solar gains to cover instantaneous heating load and storage of the remainder in embodied thermal mass or specially built thermal storage devices.
• Reduction of heat losses to the environment through use of the appropriate amount of insulation and windows with high solar heat gain factor.
• Shading control devices or strategically planted deciduous trees to exclude unwanted solar gains, which would create an additional cooling load.
• Utilization of natural ventilation to transfer heat from hot zones to cool zones in winter and for natural cooling in the summer; ground cooling/heating to transfer heat to/from the deep underground which is at a more or less constant temperature; evaporative cooling.
• Development of integrated building envelope devices such as windows which include photovoltaic panels as shading devices, or roofs with photovoltaic shingles; the dual role of these elements for electric power production and for exclusion of thermal gains increases their cost-effectiveness.
• Utilization of solar radiation for daylighting; this requires measures for effective distribution of daylight onto the work plane.
• Integration of passive solar systems with the active heating/cooling airconditioning systems both in the design and operation stages of the building.

The last requirement is perhaps the most important for the successful design and operation of a building that utilizes passive solar design principles. However, it is usually overlooked because of the absence of collaboration for integration of building design between architects and mechanical engineers. Thus, the architect may often design the building envelope based on qualitative passive solar design principles and the engineer designs the HVAC (heating-ventilation-air conditioning) system based on extreme design conditions, ignoring the benefits due to solar gains and natural cooling. This results in an oversized system, which fights the building rather than using it. The absence of collaboration between the disciplines involved in building design is decreasing with the adoption of computer tools, but the fundamental institutional barriers remain owing to the basic training of architects and engineers which does not foster an integrated design approach.

The design approach proposed in this book is based on the principle that the building and its HVAC system are one thermal system and they must be designed together based on dynamic operation, taking into account thermal storage and control strategy. For example, a variable thermostat setpoint may result in different heating and cooling equipment sizes. Thus, passive solar gains and dynamic building behaviour must be estimated quantitatively under various control strategies to design both the building envelope and the HVAC system properly for harmonious operation.

Depending on climatic conditions and building function, certain heating/cooling systems are more appropriate than others and more compatible with passive systems. For example, the thermal mass in a floor may be used both to store passive solar gains and also for a floor heating system; however, this poses a control challenge which must be carefully considered to achieve acceptable thermal comfort.

A key aspect of passive solar design is choice of the following design parameters:

• fenestration area, orientation and type
• amount of insulation
• shading devices - type, locations and areas
• effective thermal storage (insulated from the exterior environment) amount and type (sensible - such as concrete in the building envelope with exterior insulation, or latent - such as phase-change materials).

The above basic design parameters are interlinked and dependent on each other.

The ultimate design objective is minimization of energy costs (heating, cooling, electricity) while maintaining good interior thermal comfort. The thermal mass of the building causes delays in its response to heat sources such as solar gains - the well-known thermal lag effect. This effect, if taken into account in the selection of thermal mass and appropriate control strategies, does not cause thermal comfort problems. It also needs to be taken into account in heating/cooling system sizing. Night ventilation may significantly reduce the need for mechanical cooling.

This book focuses on passive solar systems integrated in the building envelope.

1.1.1 Building enclosure design principles

In implementing passive solar design techniques one must consider all other aspects of building design. A building enclosure and its components should generally be designed to provide a protected and comfortable indoor environment. Building envelope components are built to protect from the weather elements - rain, sun, winds and variations of the environmental temperature. The external envelope acts like a ‘filter’ between the external environment and the indoor space. The filtering action is best illustrated with the effect of thermal mass on the fluctuations of outside temperature, which are modulated into a small room-temperature swing. Another filtering action is reduction of noise transmission.

In addition to protection from the weather elements there is a need for a structure to support the weight of the building envelope, building contents, snow and water on the roof, and to ...

Table of contents

• Cover
• Title
• Copyright
• Contents
• Preface
• 1 Introduction and basic concepts
• 2 Transient heat transfer and thermal storage
• 3 Fenestration components and systems
• 4 Dynamic models of heat transfer in solar buildings
• 5 The passive response of buildings and its use in design
• 6 Ventilation and indoor air quality
• 7 Sizing of small auxiliary heating/cooling systems
• 8 Control of passive solar buildings
• 9 Solar energy utilization techniques and systems
• Index