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Section 1 Energy Requirements of a Building

Section 2 Alternative Heating Strategies 

 

Description:  The purpose of this unit is to enable you to analyse the buildings in terms of their heating needs and to determine heating loads. The unit will also enable you to evaluate alternate heating strategies and district heating systems.

Author:  Gates MacBain Associates


Section 1  Energy Requirements of a Building




Aims and Objectives

At the end of this section you should be able to:
  • Analyse buildings and identify their heating needs.
  • Determine space heating loads and energy requirements for heating schemes in complex buildings.


A building is made up of a number of components called elements such as walls, roof, floors, windows and doors, etc. These elements enclose the spaces but also help to protect from the cold outside temperatures. These are made of various materials each having different thermal properties. In colder climates, we have to ensure that heat does not escape and is retained within a building. We design and construct the building elements to ensure that these do not loose heat. 

Buildings also gain heat from a number of sources such solar radiations, people working inside a building, machinery and equipment.   

We can determine how much heat building is loosing and how much it is gaining. The net result will tell us about the heating requirements of a building and the amount of energy required to do so. 

In this section, we will discuss the heating requirements and how heating loads energy requirements are determined for buildings.    


Heating Requirements 

The most important factor in determining the heating requirements of a building is the heat loss which depends upon a number of factors as below:
How well the building is insulated externally. The exterior part of a building can be called as a Shell, Fabric or an Envelope.

What is the area of the building exposed externally? For example a terraced house is less ‘exposed’ than a detached one and hence will loose less heat.

What is the temperature difference between inside and outside of a building? If the difference is large, heat loss will be more, for example, when you open a door or a window.

What is the air change rate? Air can move out of a building taking heat with it. This movement can be through cracks and gaps in construction or through opening doors and windows.

How a building is used? Whether whole building is occupied all the time or there are different ‘patterns’ for various areas.
  

Heat Loss 

As described earlier, the building can loose heat through its external elements or ‘fabric’ as well as through ventilation. Add the two together and you will fins the total heat loss from a building.  

Fabric heat loss is calculated by considering individual elements and their respective areas. Ventilation heat loss is calculated by considering volume of the room and number of air changes. Both also take into account the temperature difference between inside and outside of a building.  


Heat Gains  

A building gains heat through: solar radiations; internal heat gains; and ventilation and infiltration.  

Solar radiations strike the buildings at a certain angle and intensity depending upon the location of the building. This heat is transferred inside through walls, roof and windows. Solar heat gain can be calculated by using reference tables and computer software. 

Internal heat gains are a result of number of a people in the building, what they are doing and what kind of lighting, machinery and equipment is there. 

Total heat gain of a building is the sum of all the individual heat gains.  


Energy Balance 

Once we know the heat gains and heat loss, we can determine the net heat available and decide whether building is to be heated (likely to be in winter months) or cooled (likely to be in summer months). This extra heating or cooling requires energy. We can write it as: 

Energy for heating = [Fabric heat loss + Ventilation heat loss] – [ Heat gains}  


Calculation of Energy 

Heat is a form of energy. To calculate it we need to consider the period and time of the year when it is required. When we use this energy over a certain period of time, we call it Power. The formula to calculate energy is thus:             

Energy = Power x time

Or        

E = P x t   

If we measure Power (P) in Watts and time (t) in seconds, the unit of energy is Watts seconds or Joule (J).   

Energy is also measured in Kilowatt hour (kWh) or British Thermal Unit (BTU).     


Degree-days Method   

Using this method, we can compare the heating requirements from one year to another or from one area to another area.    

Let us assume that a building’s inside temperature is always higher than the outside temperature due to the heat gain sources mentioned earlier. We can group buildings and assign them a difference value. Take the example of a modern huge office complex which has a large glazed area externally, number of people work there and there is a lot of equipment inside. If we give it a value of 6°C, it would mean that the inside temperature of the building will be 6°C higher than the outside. If we have to maintain a temperature of 21°C inside for human comfort, we can calculate what we call as Base Temperature.    

Base Temperature = 21 – 6 = 15°C   

The base temperature suggests that whenever the external temperature falls below 15C, there will be a need for heating.   

We can monitor the outside temperature and take a mean value. For example, we may find out that the outside temperature is less than 1C than the Base Temperature. This will be 1 Degree Day.   

The publications listed contain a more detailed explanation of heat losses and determining energy requirements. You are advised to read these before attempting the tasks.   

Some useful websites and video resources are listed with self explanatory titles which will help you understand the concepts.    



Websites



Publications

  • McMullan, R. (2007) Environmental Science in Buildings. 6th edition: Palgrave Macmillan, New York (Chapter 3)
  • Brumbaugh J E. (2004). HVAC Fundamentals, Vol 1: Heating Systems, Furnaces and Boilers, 4th edition: Wiley Publishing, Indiana (Chapter 2, 3 & 4)
  • Chadderton D V. (2007). Building Services Engineering. 5th edition: Taylor & Francis, England (Chapter 4)
  • Oughton D R. and Hodkinsons S. (2002). Heating and Air-conditioning of Buildings, 9th edition. Elsevier Science Ltd. (Chapter 3)
  • Moss, K. (2003). Heating and Hot Water Services Design in Buildings, 2nd edition. Spon Press



Videos / DVDs



Self-Assessment Task

  • Explain how a building loses heat.
  • Discuss the factors contributing to heat loss in a building.




Section 2  Alternative Heating Strategies




Aims and Objectives

At the end of this section you should be able to:
  • Evaluate alternative heating proposals and strategies to establish feasible design solutions.
  • Evaluate the use of district heating schemes.


Heating the buildings is a requirement for a comfortable living. However, traditional heating methods have an adverse effect on the environment by increased carbon emissions. Hence it is important that we explore alternative heating schemes or strategies. 

The basic principle is to reduce our dependence upon traditional petroleum-based fuels. Such strategies can not only help the environment but help to reduce the cost of heating. 

To introduce any alternative methods in existing buildings is challenging due to the age and fabric of such buildings and due to the potential cost involved. New-build properties offer more choices where such alternatives can be designed and are more cost effective.  

Alternative strategies are discussed below. These can be applied to the design or a new building or upgrading an existing one. It is a good idea to mix-and-match the approaches to arrive at the best possible and environment friendly solution.  


Solar Heating 

We can design our homes in a way that makes the best use of heat radiated by the sun. This approach sometimes referred to as passive solar heating includes ideas such as south-facing windows, using materials that retain heat and planting tress strategically to provide shade during the summer. 

The other way to utilize solar energy is called active solar heating. We can replace our traditional heating equipment with solar collectors, heat pumps and storage tanks. The energy source, sun, is obviously a renewable source. We can use solar panels and photovoltaic modules as collectors.   


Ground Source Heat Pumps    

There is a considerable amount of heat contained within the earth. In geothermal heating, we extract and use this energy for heating purposes. We can push a fluid down the ground to an appropriate depth. Fluid extracts heat from the ground. The fluid is then transferred to the building using underground pipes. A heat exchanger takes the out from the fluid which is distributed within the building.   

Again, the source, earth, is renewable. Geothermal systems are believed to works well on the existing properties as a retrofit.   


Air source heat pumps   

These absorb heat from the outside air rather than the ground and are classified as either air-to-air or air-to-water. These pumps are energy efficient, low-maintenance and rely upon a renewable source   

Air-to-air heat pumps are used to provide heat directly inside a building. The system consists of an ‘external’ unit used to extract heat which can then be distributed inside a building. The system is unlikely to provide hot water.   

Air-to-water heat pumps are suited where low temperature heating is required over longer periods of time such as under floor heating.     


Wood Pellet Boilers and Stoves   

We can use wood pellets for both hot water and in the stoves. These are a cheap alternative to the traditional gas or oil-based boilers and stoves. The burning efficiency is good which means that these use most of the fuel leaving a small amount of ash which does not need to be cleaned daily.   

These are considered as carbon neutral as the amount of carbon dioxide generated during burning is almost the same if this wood was allowed to decay in the forest.     


Green Roofs   

If roof a building is covered with earth, it dramatically improves its thermal properties. Building can retain heat during winter and be cooler in the summer. The term green roof (sod roof, living roof, etc) refers to a roof covered with vegetation. It consists of layers of soil and water proofing material besides other components.      


Community or District Heating   

This consists of a central boiler and a pipe distribution system to cater for a number of buildings. Each building has a heat exchanger. The system has been implemented in Scandinavia where it serves on an extensive scale.   

It can use biomass and other renewable sources of energy having low-carbon content and can be implemented at a comparatively low cost.   Other Strategies Instead of hating large areas through central heating, we can use space heaters which are self-contained device for heating an enclosed area or a small space   

Density of a material determines its capacity to store heat. Such materials heat up slowly, and then give out that heat gradually. Buildings made of brick, concrete and stone have a high thermal mass or thermal capacity. Buildings with a high thermal mass take a long time to heat up but also take a long time to cool down and hence has a very steady internal temperature which means we can have small boilers in the house which can raise the temperature gradually and then turning themselves off for sustained periods.     


The resources listed below contain a more detailed explanation of alternative heating strategies and district heating systems. These have self explanatory titles which will help you understand the concepts and their application. Some case studies are also included.    



Websites



Publications

  • McMullan, R. (2007) Environmental Science in Buildings. 6th edition: Palgrave Macmillan, New York (Chapter 3)
  • Brumbaugh J E. (2004). HVAC Fundamentals, Vol 1: Heating Systems, Furnaces and Boilers, 4th edition: Wiley Publishing, Indiana (Chapter 2, 3 & 4)
  • Chadderton D V. (2007). Building Services Engineering. 5th edition: Taylor & Francis, England (Chapter 4)
  • Oughton D R. and Hodkinsons S. (2002). Heating and Air-conditioning of Buildings, 9th edition. Elsevier Science Ltd. (Chapter 3)



Videos / DVDs



Self-Assessment Task

  • Discuss a number of alternative heating strategies evaluating their possible applications.
  • With the aid of a drawing, explain the working of a district heating system.





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