Energy Audit Report For A Residential House Reports Example
ENERGY AUDIT FOR A RESIDENTIAL HOUSE
Energy conservation is desirable for both economic and environmental reasons. Efficient energy use reduces the energy drawn from the mains. Reduction of the power load per home means that the utility company will have to supply less power to the residential estates. The utility company in turn will undertake less carbon emitting energy production activities. Efficient energy use will reduce the carbon footprint of individual residential houses and the utility company. Reduction of toxic emissions will decelerate air pollution, which leads to global warming that causes a rise in sea levels due to melting of polar ice. Melting of polar ice also threatens animals which thrive in polar habitats such as the polar bear.
Energy conservation is beneficial to the economy and individuals alike. A lot of resources are used in power generation and transmission activities. It is of a great loss when the generated power gets wasted by the final user even though he or she will pay for it. Efficient energy use ensures continuity in utility and exploitation of natural resources . Energy wasted is equivalent to wastage of economic resources. Energy generation is accompanied by external cost such as environmental degradation. Efficient use of energy is a mitigating factor to these negative externalities. Inefficient energy use raises the external costs which have to be shouldered by the public.
In my home we use electricity as the main source of energy. A utility company called npower supplies us with the grid power and charges us on a quarterly basis. The utility company sells us power under the Standard SC ROB tariff at 16.050p per kWh and a daily standing charge of 10.960p. Our daily energy consumption averages at 11.95KWh. Most of the energy used in the house goes to powering electrical devices, lighting, and space heating during winter. Our last energy bill covered 108 days and amounted to £335.04. The objective of this energy audit is to determine our home’s energy consumption and identify and recommend potential energy saving measures.
Most of the energy uses in the house are resistive loads so we consume power at an almost a unitary power factor. This means that there is no need to invest in power factor correction equipment as very little reactive power is required. The only inductance loads in the house are the fridge compressor and air conditioning air fans which present negligible reactance . During winter, a lot of energy goes into space heating due to the high current required.
There are no existing energy management measures undertaken at the moment. The possible identified energy conservation opportunities (ECOs) identified are:
Replacement of 4ft fluorescent lamps with energy efficient LED tubes
Turning off lights when not in use manually or by use of motion sensors
Reduce the number of lights in the corridors
Incorporation of a solar photovoltaic (PV) system and a solar water heating system to reduce overdependence on the grid
Use of natural lighting
The Energy Audit’s main objective was to study energy uses in the house and identify Energy Conservation Opportunities (ECOs).
In order to achieve the objective, the methodology was as follows:
The energy audit was conducted mainly to identify the possible energy saving potential of various equipment and the operations at the house.
A Walk through the entire house was done to identify the possible energy saving opportunities and take stock of energy consuming operations, and possible energy management practices.
Various specifications and operating data of electrical equipment were studied and an analysis o the electricity power bills were done.
This report incorporates analysis and energy saving opportunities identified.
FINDINGS AND DATA ANALYSIS
This chapter presents an analysis of the data that was obtained and describe the findings. The data obtained included energy consumption overall and equipment specific, Electricity bill, average monthly and daily energy consumption, and inventory of all equipment. The data gathered was aimed at answering these questions:
What types of energy sources are being used?
How much is being used?
Where is the energy being used?
How much does it cost?
What factors affect consumption?
How efficiently is the energy being converted, distributed and used?
Electronic household devices compose majority of the load. The table below represents the electrical devices and their total energy rating. Items such as the fridge operate virtually throughout the day. Other items such as the fans operate during summer while the space and water heating system operates during winter only. Other electronics such as the television get used a lot during holidays. As a result, the total load varies considerably with seasonal changes and so does the energy bills.
Overview of the energy consumption
During the audit, it was not possible to log the entire premise from the mains for a comprehensive load profile study. Analysis of the power bill was done and tabulated in the table below. The period considered for the base line information is from May 2014 to November 2014 because that is the period covered by the data available. Accordingly, the following are the general base line parameters used to establish the feasibility of the energy saving measures proposed.
Energy consumption projections
If the tariff is not switched, the projected annual power consumption bill will be
£786.88. If the suggested energy conservation measures suggested in this report are implemented, this figure is expected to reduce dramatically. The energy savings realized will help to recoup the initial investments involved in implementing the energy conservation measures.
Analysis of energy usage and losses in the house
Figure 1: Sankey Diagram showing effective energy use and losses in the house
Currently, all the energy used in the house is drawn from the mains. 80% of that power is effectively applied while 20% is lost during consumption. The biggest source of losses is the space heating system which accounts for 13% of the losses. This may be due to an inefficient heating design or inefficient heaters . Lighting losses account for 5% of the total energy. Lighting losses occur due to use of inefficient lights which convert electrical energy to heat instead of light. Use of ballast shocks also causes energy loss due to inductance . Miscellaneous energy losses are those losses caused due to leakage currents or heating of devices.
ENERGY CONSERVATION OPPORTUNITIES
Solar Energy Installation
In order to offset the current power bill, investment will be done on solar energy for water heating and electric power. All the power currently used in the house comes from the grid. Solar energy harnessing will reduce overdependence on the grid and offer flexibility and freedom in power applications.
Solar photovoltaic systems convert power from the sun to electricity through photovoltaic effect. The size of the system installed should support at least 80% of the power needs. Power produced by the solar panels will be fed to an inverter which will convert the direct current from the solar panels to alternating current applicable in electrical devices.
Grid tied type of inverter will be used for the solar PV system. This is because grid tied inverters allows storage of produced energy into the grid through net metering. Net metering is a phenomenon whereby power can flow either way on both direction of a power meter . During the day, the solar PV system produces more power than required as these are the off peak hours. The surplus power is fed to the grid. The meter logs how much power has been fed to the grid during the day and posts this as negative value. At night, the panels are not producing and power flows from the grid to the house. The meter logs this as a positive load which cancels out the negative readings recorded during the day. Net metering is advantageous because no battery banks are required for the system. Batteries are heavy, bulky, expensive, and require special care and maintenance . In case more energy is consumed from the house than is generated by the panels, the extra energy supplied will be charged in the bill. Surplus energy supplied to the grid will attract monetary compensation upon agreement and a contract with the utility company.
The daily energy consumption at the house is 11.95kWh. The solar PV system should supply at least 10KWh per day. The system should be slightly less than the required power so that the net positive power drawn from the grid can be used to synchronize the inverter output in terms of frequency and voltage.
PV system sizing and payback period calculation:
Assuming there are 6 peak sun hours in a day with an average insolation of 1kW/m2, the required number of panels will be:
Where 1.1 is the oversize factor, 6 is the number of effective sun hours in a day, and 0.953 is the panel efficiency * dirt losses* DC cable losses.
The average cost of installing solar PV system is £2.5/ Watt. The total cost of the system will be:
The payback period for a renewable energy system is based on the realized energy savings.
The energy per unit cost is 16.05p/kWh. The annual energy savings will be:
3560kWh will be generated annually, through net metering, the total energy savings will be:
The payback period:
The payback period for the solar PV system is 9.125 years. Solar panels have an average lifetime of 25 years after which efficiency decreases by 20% . This means after the initial investment has been recouped, the system will provide 16 years of free power.
ii) Installation of Solar water heating
200 liters of hot water are used daily in the house. A lot of electric energy is used to heat this volume of water given the high specific heat capacity of water pegged at 4.186 joule/gram °C. A 300L pressurized solar hot water system will be used to supplant the electrical heaters. The energy savings to be realized from solar water heating installation will be:
For raising water temperature from 20°C to 60°C, the energy required for the 300L will be given by 4.186*1000*300*40=50232000joules
The hot water is required over a duration of one hour, so energy in watts will be:
Installation of LED tubes
The normal T8 fluorescent tubes will be replaced with energy efficient white light T4 fluorescent lights. LED lights are more energy efficient and absorb less energy for the same level of illumination. Fluorescent lamps have ballast shocks which require high currents when switching on the lamp. A 60W fluorescent light can be replaced by a 36W Led light.
Reduction of the number of lights
There are more lights in the house than required. Reduction in the number of lights from two fluorescent lights to one light per room will reduce the lighting load.
Use of natural lighting
Natural lighting is the use of natural light from the sun during the day. In order for the building to maximize on natural lighting, alterations have to be made on the house structure to let in more light. The windows will be adjusted to full length, running from the floor to the ceiling for maximum illumination. Skylights will also be placed on the roof for illumination along corridors. Skylights let in light which is directly overhead. Placing them along corridors will offer ample illumination which will eliminate the need for lights.
Lighting control through motion sensors
Motion sensors detect movement and switch on the lights. If there is no movement, they will switch off the lights. Installation of motion sensors will guard against idle burning of lights in the house. A lot of energy is wasted when lights are left burning while no one is using them either through negligence or by mistake.
Currently, power used in the house is charged by the Standard SC ROB tariff. Switching to a cheaper tariff will lead to high accumulated savings. Standard SC DD – Electricity is a similar tariff but cheaper than the Standard SC ROB tariff. Switching to this tariff would lead to accumulated savings of £ 42.00 annually. The cheapest tariff on offer by the utility company is Online Price Fix Nov 2015 Elec DD – Electricity. Switching to this tariff would result to £186.36 being realized annually in savings as predicted by the utility company.
Online Price Fix Nov 2015 Elec DD – Electricity is the cheapest and thus the best option. Money saved through the use of this tariff will go towards implementation of other energy saving measures.
ANALYSIS OF THE PROPOSED ENERGY SAVING MEASURES
Figure 2: Sankey diagram of energy demand, consumption, and consumption after installation of the proposed renewable energy system
The diagram above shows energy demand in the house. The left hand side shows the particular loads and the percentage of total demand per load. The mid-section shoes mains consumption before installation of the proposed renewable energy system. After the solar PV and solar water heating system have been installed, the renewable energy systems will offset some of the energy consumed from the mains. SC ROB - Electricity
THERMODYNAMIC ENERGY ANALYSIS OF A FRIDGE
A fridge cools food items by pumping heat out into the atmosphere thereby lowering their temperature than the ambient. A refrigerant called tetrafluoroethane is used in a closed loop in fridges. The refrigerant has a low boiling point and a high condensation point so that continuous evaporation and condensation cycles occur readily and evenly at different stages of the closed loop. The refrigerant absorbs heat from items placed in the fridge and evaporates thereby lowering their temperature. The vaporized refrigerant then dumps the heat to the environment and condenses and the cycle is repeated all over again. An electric pump is used to drive the refrigerant round the cycle and force it through different stages of pressurization. High pressure encourages evaporation of the refrigerant while low pressure drives condensation .
Energy loss from a fridge occurs through conduction, convection, and radiation and involves permeation of heat into the interior of the fridge. The more the heat manages to enter the fridge, the harder the cooling system will work to expel it, and thus the more the energy used. Energy conservation in a fridge is achieved through insulation with poor heat conductors.
Figure 3: Sankey diagram of a thermodynamic analysis of a fridge
Conduction occurs when heat flows through a material which acts as a conduit. Heat flows from the surrounding environment to the inside of the refrigerator through its walls by conduction. The temperature gradient between the outside and the inside of the fridge drives heat flow from the ambient air at room temperature to inside and cooler fridge compartments. Heat conduction is determined by the thermal conductivity per unit area of an insulation material. Materials with high thermal resistance are placed in parallel with the fridge lining thereby greatly reduce energy loss . Thermal conductivity per unit area is calculated as:
Where “q” is the insulating material’s thermal conductivity, k is a constant, “A” is the total area of insulation, T the temperature gradient and L is the width of the material.
Convection occurs when heat is transferred from one place to another by a fluid such as water or air. In a refrigerator, convection is beneficial and undesirable at the same time. Convection helps in removal of heat from the cooling fins so that the system can pump more heat from the contents inside the ridge. Convection is also responsible for energy loss every time the fridge door is opened .
Convection is caused by the difference in fluid densities due to temperature differences. A cold fluid has high density and its particles are more closely packed. A warm fluid on the other hand exhibits more haphazard movement of its particles which are sparsely packed. As a result, warm fluids are lighter than cold fluids and hence hot fluids rises while cold fluids fall below the warm fluids. Heat transfer by convection is directly proportional to temperature difference and the surface area between a surface and a fluid .
Radiation is heat transfer in the form of electromagnetic waves. Radiation of a body is determined by its emissivity which is the heat rejecting capacity. White and shiny surfaces have low emissivity compared to black and dull materials. Radiation is also influenced by the surface area exposed to the outer environment and the temperature gradient between an object and its surrounding raised to the power of four . Power transferred through radiation is given as:
Energy efficiency should be at the heart of every energy user. The benefits of energy efficiency and conservation are not reaped by the individual users only, but also the public who suffer the externalities of energy generation. Also, energy conservation and energy efficient practices are of economical benefits due to energy savings. Renewable energy use reduces environmental pollution and saves consumers from recurrent energy bills. Implementation of recommendations made herein in this energy audit will ensure ample energy savings to slash energy spending by more than half and ease expenditure in the long run which will ensure sustainability of the investment.
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R. Banerjee. “Energy Auditing”. Electrical India, vol. 37, pp. 3, 13. 1997
C. Blumstein & P. Kuhn. “Energy Auditing”, pp. 277-294, Jan. 2006.
“Energy Efficiency Best Practice Programme (Great Britain)”, Detecting energy waste: A guide for energy audits and surveys in the government estate, January 01, 2002.
L. S. Marsh, S. J. Thomson, &, J. P. M. Argabright. “User-oriented home energy audit”. In: International Conference, 4., 1992, Orlando. Computers in Agricultural Extension Programs: Proceedings. St. Joseph, Mi: Asae, Jan. 1992.
T. Deutscher, H. Munro & G. H. G. McDougall. “Residential home energy audits: Design and implementation”. Consumer Behavior and Energy Policy. an International Perspective / Edited by Eric Monnier [e Altri], (n.d.).
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