Passive solar heating is the concept and practice of capturing, storing and consuming heat from the sun using non-mechanical systems. This article discusses passive solar heating definition, working principle and comparison as outlined below;
Passive Solar Heating Definition: 4 Ways to Define Passive Solar Heating
The above is a most basic passive solar heating definition, which highlights the absence of mechanical elements in passive systems.
To provide better understanding of the concept, it may help to make reference to the difference between active and passive solar heating systems, in form of a summarized active vs passive solar comparison. This is done in the alternative passive solar heating definition below;
Passive solar heating is a non-mechanical approach to the use of electromagnetic waves in solar radiation for heat-application purposes, which is simpler and cheaper but less effective than the fluid-mechanics-based active solar heating approach.
In passive solar heating, the systems used are usually building-integrated; meaning that they are part of the basic structure and design of buildings . Below is an alternative passive solar heating definition that makes due reference to passive solar heating systems;
Passive solar heating is an energy-transfer function carried out by passive solar heating systems, which comprise of passive solar design elements that are created and assembled in order to increase the energy efficiency and conservation capabilities of buildings, and reduce their reliance on non-renewable energy resources .
Lastly, the passive solar heating definition can be outlined based on some relatable examples of passive solar heating;
Passive solar heating is the practice and process by which thermal energy from the Sun is captured and utilized without mechanical circulation, as can be observed in any of various examples like; sunroom space heating by direct gain, passive water heating in exposed reservoir, solar greenhouse warming, thermal mass-absorption using trombe wall, and indirect solar heat gain in solarium.
How A Passive Solar Heating System Works
Passive solar heating systems are made to increase the comfort of building interiors, by capturing significant amounts of solar infrared radiation, retaining a portion of this radiation, and releasing the stored energy at other times when it is needed.
Basically, passive solar energy works by a process of solar projection, collection, absorption, and utilization; which results in visible light and heat from the Sun being used for lighting and temperature regulation respectively, in the absence of any working fluid, hydraulic pump, or turbine.
A passive solar heating system works in three basic steps which are; solar collection, retention, and release/utilization; all of which sum up to a renewable process of energy gain, conservation and consumption.
The working principle of passive solar heating systems differs from that of passive solar energy itself only in the omission of solar projection step, as this does not involve the system at all.
For most passive solar heating systems, a core objective is to maximize gain and minimize energy waste or loss, by any of the three main types of thermal transfer (conduction, convection and radiation).
Below is a brief outline of how passive solar systems work;
1). Solar Collection (in explanation of How Passive Solar Heating Systems Work)
Solar collection is the first basic step in the working principle of any given passive solar system like a solarium or sunspace.
It is simply the process by which electromagnetic rays from the Sun are captured by a body or object in sufficient quantity to be used for energy-production.
The efficiency of solar collection is a probabilistic quantity that depends on multiple factors. These include climate, latitudinal position, elevation, orientation and design.
For buildings to optimize their passive solar collection, it is generally recommendable for them to have a southward-inclined orientation, where sunlight can penetrate the building through its apertures, such as south-facing windows .
Other passive solar heating systems like water reservoirs may use a similar principle, where they must be positioned for maximum (or optimal) exposure to EM waves from the Sun.
As earlier stated, various factors determine how effective passive solar collection will be Ideal conditions for maximum gain include un-obstructed, non-cloudy atmosphere, favorable location and climate (that is, long-term average weather condition).
The amount of solar radiation that is captured directly influences the overall productivity of the passive solar heating process.
2). Heat Retention
The essence of passive solar heating is to absorb and retain a significant amount of thermal energy in solar radiation.
Heat retention in passive solar heating systems is the process whereby thermal energy in solar radiation is used to energize the atoms of a given material, so that these atoms remain energized and the heat retained, for significant lengths of time.
An important parameter in the assessment of heat retention by passive solar heating systems is the thermal mass; which is a measure of the heat-retention capacity and efficiency of material per unit mass .
It is common for the materials themselves (used to retain heat) to be described as thermal masses; and an example is the trombe wall; a passive building component that is designed to absorb and store notable amounts of radiant heat from the Sun .
Materials like concrete, stone, wood, and some types of tile are installed in passive heating systems for thermal absorption.
In the case of passive solar water heating; the water itself acts as an energy storage medium that absorbs and retains heat captured by the system. Depending on the amount of heat collected and retained, passive solar-heated water can be put to multiple uses that range from industrial to domestic.
In buildings, heat retention is helped by other design components for insulation; such as double-glazing windows. Shutting these windows before sunset can help keep in much of the heat absorbed during the day, hence saving energy costs for temperature regulation.
3). Heat Release/Utilization (in explanation of How Passive Solar Heating Systems Work)
The final stage in passive solar heating is the release of stored thermal energy.
As stated earlier, the aim of passive solar heating in buildings is to make the interior of these buildings more comfortable for occupants. This means that passive solar is not an instantaneous concept that alters temperature rapidly, as is done by electric-powered space heaters, mechanical blowers or fans.
Stored thermal energy is released and distributed within the passive solar heating system to regulate its internal temperature and minimize the rate of heat loss when external solar radiation is no longer available.
This is ideal for regions with rapid fluctuation between high and low temperatures in the day and night, as is the case where a desert climate is prevalent. It is only necessary to regulate the capture and absorption of heat during the day as well, to prevent overheating when external solar radiation is high.
Difference Between Active and Passive Solar Heating Systems
The main difference between active and passive solar heating systems is in their modes of operation; where active systems use mechanical devices like blowers, pumps and turbines; while passive systems depend solely on the energy transfer mechanism of solar radiation.
Passive solar water heaters differ from active solar water heaters by having no equipment to induce water flow. Active solar water heaters usually feature pumps or other equipment that circulate and distribute the water during and after heating.
In passive solar systems, the only mechanical processes are those which are induced by solar heating, such as the convective cycling of gaseous or liquid fluids as they are being heated.
Due to their lack of external and mechanical components, passive solar heating systems are much simpler and cheaper than active systems (both for installation and maintenance).
The table below summarizes the difference between active and passive solar heating systems;
Active Solar Heating System
Passive Solar Heating System
Space Heating, Water Heating
Passive solar heating is the use of simple, building-integrated materials and designs to collect and store solar heat for use.
A passive solar heating system works in three main steps which are;
1. Solar Collection
2. Heat Retention
3. Heat Release/Utilization
The difference between active and passive solar heating systems is that active systems include external/mechanical components, are more complex and expensive, and have more potential uses than passive solar heating systems.
1). Aisya, V.; Hendrarsakti, J. (2018). “Computational and analytical study of Trombe wall configurations within Bandung weather condition.” AIP Conference Proceedings 1984(1):020019. Available at: https://doi.org/10.1063/1.5046603. (Accessed 22 April 2023).
2). Cremers, J.; Binder, M. (2016). “Passive solar energy use.” Building Openings Construction Manual (pp.170-189). Available at: https://doi.org/10.11129/9783955532994-010. (Accessed 22 April 2023).
3). O’Brien, W. (2014). “Solar Design Days: A Tool for Passive Solar House Design.” ASHRAE Transactions 120(1):101-113. (Accessed 22 April 2023).
4). Sharaf, F. M. (2020). “The impact of thermal mass on building energy consumption: A case study in Al Mafraq city in Jordan.” Cogent Engineering 7(1). Available at: https://doi.org/10.1080/23311916.2020.1804092. (Accessed 22 April 2023).
5). Sobczyk, W.; Sapa, K. (2016). “Energy balance in a passive solar building. An attempt at economic assessment.” E3S Web of Conferences 10:00086. Available at: https://doi.org/10.1051/e3sconf/20161000086. (Accessed 22 April 2023).