The Science of Thermal Energy: Heat Transfer
The science of heat transfer and how it can be managed in buildings is often perceived as complex but, it’s not. Harnessing thermal energy brings huge benefits: improving energy efficiency; reducing operating costs; increasing the lifecycle of mechanical systems, enhancing asset value, and even providing trading and revenue generation possibilities. Our blog series, The Science of Thermal Energy outlines answers to the most frequently asked questions from developers, engineers, architects and facility managers.
In this article we focus on the fundamentals of heat transfer, and how managing it improves energy efficiency, operating costs and security of supply. If you would like to know more, feel free to get in touch.
Did you know?
- 50% of firms in British Columbia expect to build green mid- to high-rise residential projects in the next three years, compared to 32% in Ontario and 15% in Alberta.
- Shares of major energy sources used in commercial buildings in the USA include: electricity (61%), natural gas (32%), fuel oil (2%); district heat (5%);
- In Europe there are over 4,174 district heating geo-thermal systems operating across 3,731 cities. Geo-thermal, a solution capable of producing heating, cooling and electricity, is one of many sustainable thermal energy options available to help reduce the environmental footprint of our buildings. Geothermal systems can be used for low temperature heating/cooling exchange or for high temperature steam extraction for electricity generation.
- In addition to cost savings, one of the top benefits of investing in environmentally friendly mechanical systems is creating a positive tenant experience. For institutional owners the key driver is the ability to influence the market and lead by example.
What is heat transfer in buildings?
There are three modes of transfer when it comes to thermal energy in buildings. These are:
- Conduction – the flow of heat through a material by direct molecular contact. This occurs in a material or through two connected materials. Within buildings the process happens between walls, floors, piping, ducts, roofs etc.
- Convection – the transfer of heat by the molecular movement of liquids or gases. Within buildings it occurs by:
- Air replacement e.g. ventilation or air leakage (infiltration);
- Fresh or used domestic water, combustion air (including flue gases), and fluids feeding heat pumps.
- Latent heat transfer through water or water vapor transportation.
- Radiation – the transfer of heat by electromagnetic waves through a gas or vacuum. Radiation requires a line of sight connection between surfaces. Within buildings the process occurs when waves from the sun hit a window and transfers heat to that window.
Is thermal comfort tied to one, some or all the heat transfer modes?
The answer is all. Conduction, convection, and radiation heat transfer is always taking place. The illustration below demonstrates this: (to the left) conduction takes place through opaque envelope assemblies e.g. walls, floors; (center image) convection results from wind or pressure-driven air movement; and radiant heat transfer (to the right) occurs when the sun’s rays pass through windows and doors. Utility-grade, clean technology Heating Ventilation Air Conditioning (HVAC) systems provide added efficiencies and enable buildings to harvest, store, re-use and even trade their thermal energy.
With so many questions surrounding thermal energy – the how, what, why, benefits and payback – why not drop us a line? Contact firstname.lastname@example.org.
The Science of Thermal Energy: Measurement and Management
Technical insights and facts courtesy of CaGBC Canada Green Building Trends: Benefits Driving the New and Retrofit Market, US Energy Information Administration: Use of Energy in the United States Explained, GeoDH: Geothermal District Heating Potential in Europe and AutoDesk (Sustainability Workshop).