Looking At Low Zero Carbon Technologies Construction Essay

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Since there has been more awareness of the seriousness of global warming, UK legislation, building regulations, planning consent and corporate environmental policies have driven the industry to deliver low carbon plant room solutions. In addition, UK commitment to the Kyoto Protocol, an international agreement linked to the United Nations Framework Convention on Climate Change, drives the industry to reducing green house gases. Low and zero carbon (LZC) system is one of the solutions and thus has been increasingly installed in buildings, e.g. small-scale and micro-CHP units. The delivery of reduced carbon emmision of these systems contibute to the slow-down of global warming. These systems are also attractable to householder and contractors for public sector building or charitable body who want to meet the grant requirements in the low carbon building programme. These systems are praticable for different uses dependent on thermal load demand, geological conditions, installation and maintenance cost. The advantages and disadvantages of various low- or zero-carbon (LZC) technologies for generation of heat is justified in table ??

http://www.planningportal.gov.uk/uploads/br/BR_PDF_PTL_ZEROCARBONfinal.pdf

http://www.igem.org.uk/download/document/Yan_Evans_EUC08.pd

http://unfccc.int/kyoto_protocol/items/2830.php

Comparison of low and zero-carbon (LZC) technologies in terms of carbon savings, cost effectiveness and local impact. (From Throne)

Technology

Primary output

Carbon savings

Cost effectiveness

local impact

Combined heat and power, fuelled by:

Gas

Heat and electricity

Medium

Medium

Low-medium

Biomass

Medium-high

Medium

Low-medium

Solar thermal systems

Heat and electricity

Low-medium

Medium

Low-medium

District heating

Heat

Medium-high

Medium

Low

Biomass boiler

Heat

High

Medium

Medium

Ground energy systems

Open loop

Heat

Depends on building type

Depends on building type

Low

Closed loop

Heat

Medium

Medium

Low

Justification of various low or zero carbon technologies.

Technology

Description

Advantages

Disadvantages

Combined heat and power, fuelled by:

-Gas

-Biomass

heat is captureed in electrical generation and supply to local buildings

-make use of the heat waste which increase efficiency of the power generation system

-low conversion efficiencies compared to heat only systems

-great initial investment is required

-maintenance cost s high

Solar thermal systems

make use of the sun's energy to heat the water

- the systems can fit into existing buildings. It does not affect land use.

-free of greenhouse gases

- large area of collectors is required.

- dependent on geography

- limited to daytime hours and non-cloudy days.

District heating

burn biomass to feed energy from a centralised location to a number of units

-an established and tested technology

-more efficient than individual domestic boilers

-do not require individual fuel storage

-maximises dwelling space

-require long term planning

-around 10% of heat is dissipated in distribution

-agreement between mutilple private users can be complex

-Boilers are large and expensive

-the systems is still being developed, reliability has not been proven

Biomass boiler

usually burn wood chip fuel in a small boiler to generate heat for domestic scale.

-an established and tested technology

-installation is relatively easy

maximises dwelling space

-Boilers are expensive

-require more space than gas boilers

-flue require regular cleaning

-wood burning can lead to pollution issue

-feed supplay blockages to the boiler can be common

Ground energy systems:

Open loop

Closed loop

make use of the constant temperature underground to provide heating and cooling to buildings

-long life-time

-visually unobstrusive

-high COP(coefficient of performance)

-no toxic gas emmision

-energy from the ground is constant and free

-low-maintenance system

-the system is multi-functional

-reliable and cost-effective

-good building insulation is required.

-installation is costly

-dependent on geography

-boreholes can destablize the ground surface

-repairing can be complex

-refrigerants used can leak into the atmosphere and pollute the environment

Ground energy systems are worldwide and there is a wealth of successful applications from domestic to major public sector buildings. Under successful design and operation, the systems can have far more benefits than other LZC systems. There is a high significant potential to apply ground energy systems to improve environmental performance of buildings.

Open and Closed Loop Systems

Ground energy systems have two dinstinctive approaches dependent on site conditions, they are open-loop and closed loop systems. Both systems have been widely used in other European countries. The technologies have been established and tested for years. The advantages and disadvantages of open-loop and closed-loop systems are summarised in table ? The choice of choosing such systems in the initial design appraisal play an important part in the success of setting up the GSHP systems. First time consumers can understand the concepts and praticability of these systems by comparing them in different aspects of characteristic.

Characteristic

Open-loop systems

Closed-loop systems

Requirements for groundwater abstraction and reinjection

All open-loop systems include abstraction and discharge of groundwater. This process is unsustainable as the waste water discharged can pollute the groundwater reservoir.

Groundwater abstraction and reinjection are not required.

Regulatory constraints

The abstraction and discharge of groundwater is strictly regulated by the Environment Agency. Such legislation contrains the feasibility of these systems in some locations.

There liitle or no regulation for closed-loop systems. One relevant concern is to ensure that the boreholes are adequately sealed or grouted to prevent the leakage of the toxic refrigerant from the ground loop pipes.

Dependence on favourable hydrogeological conditions

Open-loop systems are only practicable when significant water-bearing strata,eg. aquifers are present beneath or near the site.

Closed-loop systems do not require the presence of an aquifer and are practicable in a wide range of geological conditions.

Number and capacity of boreholes

Relatively small numbers of abstraction boreholes can supply large demands under favourable hydrogeological conditions where groundwater yields are constant. For example, a borehole yielding 24 litre/sec can provide a peak thermal output of 500 kW.

Closed-loop systems typically require a much greater number of boreholes to yield the same peak thermal capacity compared to open-loop system. A typical 100 m deep closed-loop borehole can yield a peak thermal output of 4-7 kW.

Requirements for heat transfer system

Dependent on the heating or cooling demand. Open-loop systems can operate in cooling mode without a heat pump. Energy efficiency is improved as there is no additional energy requirement to power the heat pump compressor.

Closed-loop systems almost always use heat pumps to enhance the heat transfer as heat extration is relatively low.

Ability to handle annually imbalanced thermal loads

As open-loop systems can control the rate of groundwater disposed of to the ground, it can operate successfully with very unbalanced thermal loads. It doesn't matter where heating or cooling demand dominates the annual cycle. The reinjection of water benefits it from co-ordinating the balance of thermal load. However, the discharge water can migrate and affect the temperature of the injection water which reduces system efficiencies.

Closed-loop systems work best where annual heating and cooling load is approximately balanced. If the thermal load is unbalanced there is a long-term risk in ground temperature change. The recovery of the ground temperature has to be concerned.

Potential for off-size thermal impacts

There is potential that the warmer/cooler water can migrate to the surface water source and casue environment impacts. This impact is due to the continuous aquifer reinjection of cooler/warmer groundwater over extended periods. It can affect the habitat of wildlife and also ecology.

Heat flux in the ground is predominantly by conduction. Therefore, migration of ground heating and cooling is very slow. The off-site thermal impacts is significantly low.

Constraints on location of boreholes making up the ground element

Although open-loop systems typically require small numbers of boreholes, boreholes are preferably spaced as widely apart as possible to minimise interference between themselves. The distance between the abstraction and reinjection boreholes has to be especially considered to avoid thermal disturbance.

A large number of boreholes are required for closed-loop systems. They need to be arranged on a grid pattern to maintain a minimum horizontal separation between boreholes. The recovery conditions of the ground temperature has to be taken into account.

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