ENVIROMENTAL SCIENCE

ENVIROMENTAL SCIENCE

Introduction

Basically heat transfer refers to process of thermal exchange between different systems. Generally the heat transfer from two systems will be from the hotter region to the cooler one. Now when we discussing about heat transfer in buildings it is important due to the fact that it’s used for designing fabric and also for designing passive and active systems necessary to deliver the required thermal conditions for minimum consumption of resources. Very broadly mechanisms of heat transfer can be described as convection, conduction, radiation and phase change. The thermal behavior of a system is a function of dynamic relationship of the mechanisms.

Describing Building Heat Mechanisms

conduction; this is the diffusion of internal heat within a body as a result of temperature difference across it. Conduction in building is important where there may be temperature differences between the inside and outside of a building for instance in a heated building during winter(Chadderton, D. 2013) . This mechanism is the main potential heat transfer in which internal heating and cooling can be lost to the outside resulting into occupant’s discomfort, high carbon emissions and even may result into high operation cost. Conduction in buildings can be inhibited by insulating materials that have high thermal resistance which will in turn help rescue heat transfer between the inside and outside.

This insulating effect can also be achieved by thermal mass of building components. By thermal mass we basically mean the ability of material to absorb, store and release heat energy. This can be used in even out variations in internal and external conditions, absorbing heat as temperature rises and releasing it as they fall (Portman, J. 2016). In building design its useful in evening-out and delaying extremes in thermal conditions, stabilizing the internal environment and so reducing the demand for building services systems.

convection; this is the movement of fluid such as air by advection and diffusion .This is important in design building where movement of air is necessary to moderate internal temperatures, reduce accumulation of moisture odors and other gases that can build up during occupied periods(Chiu, B. & Lai, J.  2016). Convection in building designs is also important in improving comfort of occupants. Significantly this mechanism is a heat transfer resulting from movement of air of different temperatures.

Air movement in a building can be natural or forced .For instance it can be forced by driving it with fans according individuals taste. By natural it means it could either be wind driven or buoyancy driven which in both cases results into pressure differences from one part of the building to the other(Coley, D. 2017). It can be extremely complicating when one needs to determine the exact movement of air within buildings as it requires use of computational fluid dynamics  (CFD).Notably fluids can be used to transfer heat within buildings through mass transfer ;for example by flow of a refrigerant, chilled water or hot water around building to provide heating or cooling.

Radiation; Generally all bodies which are hotter than zero degree Celsius emit thermal radiation .They also emit thermal radiation emitted by their surroundings. The difference is the amount of radiation emitted or absorbed by a body at any given moment may result in a net heat transfer which will produce a change in the temperature of that body .In a built environment, the range of terrestrial temperatures is relatively small and relative to the temperature of the sun; this range is so cold and so radiating at a long wavelength compared to the sun. so surfaces in a built environment will tend to absorb solar radiation and emit long wave infra-red radiation.

This difference also produces effects such as greenhouse effect. The atmosphere is relatively transparent to solar radiation, which means it allows sunlight to enter the atmosphere and heat the earth surface(Chadderton, D. 2013) These surfaces then re-radiate heat as long wave infra -red radiation which greenhouse gasses tend to absorb rather than emit. The result is that the long wave length infra-red radiation is trapped and heat accumulates in the atmosphere causing warming process.

Phase change; Basically when substances change phase , for instance from liquid to gas they absorb or release heat energy .For example when water evaporates , it absorbs heat producing a cooling effect, and when it condenses it releases heat .So when water evaporates from surface of a building it has a cooling effect(Portman, J. 2016). This process is important in refrigeration where refrigerant gases absorbs heat from the cooling medium typically water as they evaporate and when they   condense they release heat which is rejected to the outside. phase change materials are used in constructions to reduce internal temperature changes by storing latent heat in the solid liquid or liquid gas phase change of materials.

Example

Calculate the total heat loss from the building shown above shows the fabric and ventilation losses.

Rectangular Building dimensions: 6.0 meters long x 3.0 meters wide x 2.5 meters high.

The window size is 2.0 m long x 1.0 m high.

The air change rate due to natural ventilation is 2 air changes per hour.

It is normal to ignore the door without glazing and add it into the wall area in most calculations although for very accurate methods the door could be calculated separately.

Q       =        ‘U’. A. dt

First calculate the heat loss through the window

Q window            =          2.8 x 2.0 x 1.0 x (20 – – 2)

Q window            =          2.8 x 2.0 x 22

Q window            =          123.20 Watts

Second calculate the heat loss through the block work.

Q front wall         =          0.317 x (15.0 – 2.0) x (20 – – 2)

Q front wall         =          0.317 x 13 x 22

Q front wall         =          90.66 Watts

Q rear wall           =          0.317 x 15 x 22

Q rear wall           =          104.61 Watts

Q side walls         =          0.317 x 2 (3.0 x 2.5) x 22

Q side walls         =          104.61 Watts

Q walls total        =          90.66 Watts + 104.61 Watts + 104.61 Watts = 299.88 Watts

Third calculate the heat loss through the floor.

Q floor                  =          0.7 x 6.0 x 3.0 x 22

Q floor                  =          277.20 Watts

Fourth calculate the heat loss through the roof

Q roof                   =          0.8 x 6.0 x 3.0 x 22

Q roof                   =          316.80 Watts

Fifth calculate the heat loss by ventilation

Q     =          N. V . Sp.ht. . dt

Q     =          2.0 x 6.0 x 3.0 x 2.5 x 0.34 ( 20 – – 2)

Q     =          2.0 x 45 x 22

Q     =          673.2 Watts

Finally calculate the total heat loss

Q total = heat loss window + heat loss block work + heat loss floor + heat loss roof + ventilation heat loss

Q total           =          123.20 + 299.88 + 277.20 + 316.80 + 673.2

Q total           =          1690.28 Watts

It can be seen from the above calculations that the ventilation heat loss accounts for:

( 673.2 / 1690.28) x 100 = 40% of the total heat loss for the building.

It is therefore important to establish an accurate figure for the air change rate and to minimize unnecessary infiltration and exfiltration in buildings.

II; comparing the provision of natural and artificial lighting within buildings

when discussing about the provision of light within buildings either natural or artificial , there are number of things that are put into concern(Chadderton, D. 2013). To start with ,natural lights are produced by the sun while artificial light sources can be from incandescent bulbs, fluorescent bulbs and lights emitting diodes(LEDS).Although artificial  many light do not radiate a full spectrum of colures which could inhibit plants growth ,full spectrum bulbs are available which mimic natural sunlight are  available.

Natural light which produces heat and colure comes from radiation given off by the sun .It is then filtered through the earth atmosphere and absorbed by plants. Artificial light sources can consist of  filament that uses electricity or halogen gas to glow or an electronic device that emits ligh(Portman, J. 2016). Some artificial light uses gas or electricity to produce light. Unlike natural light ,artificial lighting intensity can be adjusted to serve the needs of individual plants.

2;Discussing the Influence of Building and its Services on the Internal Acoustic Environment and Comparing Calculated Noise Level with Recognized Design Criteria.

The acoustical environment of a workplace is given little or no attention during project design and plan. The functionality and  aesthetics of the` workplace are usually the primary focus of the designer. The factors contributing to the productivity of the employees occupying the workplace are too much overlooked. Providing comfortable environment for employees contributes to reduced absenteeism and also optimum performance(Chiu, B. & Lai, J.  2016). Workspace comfort includes a number of factors like day lighting, electric lighting indoor environmental quality , temperature and acoustics. The assault on ears in the workplace  can come from traffic noise outside , mechanical equipment in adjacent spaces ,copiers  and voices within the workplace.

Besides the design team’s focusing on the project’s functionality and aesthetics, building acoustics is so often given low priority because it competes for limited project dollars with a number of other project goals, including: sustainable design, development, physical security, anti-terrorism, information technology, telecommunications, and building automation and controls.

Though there are some differences in the acoustical requirements of offices, classrooms, and conference rooms, several common noise problems affect these occupancies: Like for instance too much noise entering the space or the adjacent spaces or basically lack of sound control entering the space itself(Chadderton, D. 2013). Therefore noise in these occupancies is typically not at a high enough level to be harmful to human hearing. Rather, the noise is distracting from concentration on work or study and provides less than ideal working and learning environments. Below is a calculated comparison of noise level in a recognized design criteria.

3;Explaining the Operation and Control of the various Components which make up Particular H.V.A.C Engineering Systems Considering the Impact of the System Choice and Sustainability.

HVAC is an acronym for ‘Heating, Ventilation and Air-conditioning’. It can also be thought of as a climate-control mechanism to ensure that humidity and temperature are properly regulated in a living environment. A basic knowledge of HVAC systems includes the principles of system operations, and understanding of the factors that determine the capacity of the equipment and also the various components that make up a HVAC system(Portman, J. 2016). So there is basically a need to have this basic knowledge prior to installations or doing any upgrading(Hens, H.  2017). It  is an important part of residential structures such as single family homes, apartment buildings, hotels and senior living facilities, medium to large industrial and office buildings such as skyscrapers and hospitals, on ships and submarines, and in marine environments, where safe and healthy building conditions are regulated with respect to temperature and humidity, using fresh air from outdoors.

The three central functions of heating, ventilation, and air conditioning are interrelated, especially with the need to provide thermal comfort and acceptable indoor air quality within reasonable installation, operation, and maintenance costs. HVAC systems can be used in both domestic and commercial environments(Chadderton, D. 2013). These systems can provide ventilation, and maintain pressure relationships between spaces. The means of air delivery and removal from spaces is known as room air distribution. There are basic factors that determine the capacity of HVAC system required. Some of them include;

Heating: This is the amount of thermal energy that needs to be added to the space. It mostly makes use of heaters. These are appliances whose purpose is to generate heat that is  warmth for the building. This can be done via central heating. Such a system contains a boiler, furnace, or heat pump to heat water, steam, or air in a central location such as a furnace room in a home, or a mechanical room in a large building(Portman, J. 2016). The heat can be transferred by convection, conduction, or radiation. Heaters exist for various types of fuel, including solid fuels, liquids, and gases. Another type of heat source is electricity, normally heating ribbons composed of high resistance wire .

Electrical heaters are often used as backup or supplemental heat for heat pump systems. Initially, heat pump HVAC systems were only used in moderate climates, but with improvements in low temperature operation and reduced loads due to more efficient homes, they are increasing in popularity in cooler climates. In the case of heated water or steam, piping is used to transport the heat to the rooms(Chiu, B. & Lai, J.  2016). Most modern hot water boiler heating systems have a circulator, which is a pump, to move hot water through the distribution system. The heat can be transferred to the surrounding air using radiators, hot water coils , or other heat exchangers. The radiators are  mounted on walls or installed within the floor to produce floor heat. The use of water as the heat transfer medium is known as hydronics.

The heated water can also supply an auxiliary heat exchanger to supply hot water for bathing and washing. There are a number of dangers attached to this system .For instance the use of furnaces, space heaters, and boilers as a method of indoor heating could result in incomplete combustion and the emission of carbon monoxide, nitrogen oxides, formaldehyde, volatile organic compounds, and other combustion byproducts(Coley, D. 2017). This incomplete combustion occurs when there is insufficient oxygen and thus the results are  harmful byproducts, most dangerously carbon monoxide, which is a tasteless and odorless gas with serious adverse health effects. The primary health concerns associated with carbon monoxide exposure are its cardiovascular and neurobehavioral effects. It  can lead to hardening of arteries  and also trigger heart attacks. Thus calling for proper ventilation which will in turn maintain proper indoor air quality .

Dehumidifying; This is the process of removing water vapor from a given space. It is also an air conditioning system provided by the evaporator. Basically  the evaporator operates at a temperature below the dew point, moisture in the air condenses on the evaporator coil tubes. This moisture is collected at the bottom of the evaporator in a pan and removed by piping to a central drain or onto the ground outside. This system also uses a device known as dehumidifier which controls humidity of a room or a building(Hens, H.  2017). It is often employed in basements which have a higher relative humidity because of their lower temperature .For example it is highly effective in food retailing establishments and even large open chiller cabinets. This system also requires some basic maintenance as they are equipped with air filters .These air filters are lightweight gauzy material, and must be replaced or washed as conditions warrant.

For example, a building in a high dust environment, or a home with furry pets, will need to have the filters changed more often than buildings without these dirt loads(Chadderton, D. 2013). Failure to replace these filters as needed will contribute to a lower heat exchange rate, resulting in wasted energy, shortened equipment life, and higher energy bills; low air flow can result in iced-over evaporator coils, which can completely stop air flow.

Additionally, very dirty or plugged filters can cause overheating during a heating cycle, and can result in damage to the system or even fire. In addition to replacing the air filter at the evaporator coil, it is also necessary to regularly clean the condenser coil. Failure to keep the condenser clean will eventually result in harm to the compressor, because the condenser coil is responsible for discharging both the indoor heat which is  picked up by the evaporator and the heat generated by the electric motor driving the compressor(Portman, J. 2016).

Air filtration and cleaning; In this system it deals with purifying the air by removing the dust ,pollen and other pollutants. Air cleaning and filtration removes particles, contaminants, vapors and gases from the air. The filtered and cleaned air then is used in heating, ventilation and air conditioning. Importantly it should be taken in account when protecting our building environments. Taken to the note is the clean air filter rate and filter performance. This take to account the amount of clean air an air cleaner provides to a room or space. For example, an air cleaner with a flow rate of 100 cubic feet per minute and an efficiency of 50% has a clean air delivery rate of 50 cfm. Along with clean air delivery rate, filtration performance is very important when it comes to the air in our indoor environment(Chiu, B. & Lai, J.  2016). Filter performance depends on the size of the particle or fiber, the filter packing density and depth and also the air flow rate.

4;Important environmental design criteria that building services systems must achieve and maintain to ensure occupant thermal comfort.

Building construction and operations can have extensive direct and indirect impacts on the environment, on society, and the economy. Thus there are number of design solutions which the designers must achieve in order to balance the environment ,society and the economy needs(Coley, D. 2017). So there is need to reduce or completely avoid depletion of critical resources like energy, water, land, and raw materials; prevent also environmental degradation caused by facilities and infrastructure throughout their life cycle; and create built environments that are livable, comfortable, safe, and productive.

Buildings use resources such as energy, water, raw materials, etc,and also  generate waste that is occupant, construction, and demolition. This situation makes the  building owners, designers, and builders each to face unique challenges in order  meet demands for new and renovated facilities that are accessible, secure, healthy and productive(Chadderton, D. 2013), while minimizing any negative impacts upon society, the environment, and the economy.

In addition , for sustainable design concepts in new construction, sustainable design advocates should encourage retrofitting existing buildings rather than building a new. Retrofitting an existing building can often be more cost-effective than building a new facility. Designing major renovations and retrofits for existing buildings to include sustainable design attributes reduces operation costs and environmental impacts, and can increase building resiliency(Portman, J. 2016). The embodied energy of the existing building is squandered when the building is allowed to decay or to be demolished. There are a number of principles that a designers should put into concern in order to meet occupant thermal comfort.

Amongst them include proper site selection. The location, orientation, and landscaping of a building affect local ecosystems, transportation methods, and energy use. Incorporating smart growth principles into the project development process is important whether a project is a single building, a campus, or a large complex such as a military base. Siting for physical security is a critical issue in optimizing site design, including locations of access roads, parking, vehicle barriers, and perimeter lighting(Chiu, B. & Lai, J.  2016). Whether designing a new building or retrofitting an existing building, site design must integrate with sustainable design to achieve a successful project. The site of a sustainable building should reduce, control, and treat storm-water runoff. If possible, strive to support native flora and fauna of the region in the landscape design.

The other principle is enhancing indoor  environmental quality. This means that the whole project must and should favor the occupant’s health ,comfort and productivity. Among other attributes, a sustainable building maximizes day lighting, has appropriate ventilation and moisture control, optimizes acoustic performance, and avoids the use of materials with high-Volatile organic Compounds emissions(Coley, D. 2017).

The other factor is optimizing the operational and maintenance practices of the building . This factor contributes to  improved working environments, higher productivity, reduced energy and resource costs, and prevention of system failures(Chadderton, D. 2013). Encourage building operators and maintenance personnel to participate in the design and development phases, to ensure optimal operations and maintenance of the building and the features such as storm water facilities designed to reduce the impact of the building on the land. One can also recruit develop, and train highly skilled maintenance personnel to operate increasingly and  sophisticated high-performance buildings.

Designers can specify materials and systems that simplify and reduce maintenance requirements ,for instance  which  require less water, energy, and toxic chemicals cleaners to maintain; and are cost-effective as well as  reduce life-cycle costs(Portman, J. 2016). Also design facilities to include metering, to track the progress of sustainability initiatives, including reductions in energy and water use and waste generation, in the facility and on-site.

Conclusion

The other important factor to put in place is optimizing the use of energy. Find appropriate ways to reduce energy load, increase efficiency, and maximize the use of renewable energy sources in federal facilities(Hens, H.  2017). Try improving the energy performance of existing buildings as it is  important to increasing  energy independence.

Reference

Chadderton, D.V., 2013. Building services engineering. Routledge.

Portman, J., 2016. Building Services Engineering: After Design, During Construction. John Wiley & Sons

Chiu, B.W. and Lai, J.H., 2016. Implementing Building Information Modelling in Building Services Engineering: Benefits and Barriers. Building up business operations and their logic Shaping materials and technologies, 3

Coley, D., 2017. ‘The building performance gap: Are modellers literate?’–Response of the author. Building Services Engineering Research and Technology, 38(6).

Hens, H.S., 2017. Building physics-heat, air and moisture: fundamentals and engineering methods with examples and exercises. John Wiley & Sons.

.