Energy Management - System and Energy Saving Requirements

Steve Goddard

Energy Management – Assignment 3 System and Energy Saving Requirements Q3.1 Assess systems which will provide an energy analysis Describe how the use of combined heat and power (CHP) and combined cycle gas turbine (CCGT) will reduce losses and therefore save energy and money if introduced into a local power generation system. Integrated systems for CHP in buildings are beneficial to the building owners as well as the society in general and the nation. Benefits to building owners for deploying CHP systems for buildings include the following: Reduced energy costs Building owners can reduce their energy costs by deploying CHP systems because compared to conventional systems these systems provide the following advantages: • • •

Increased energy efficiency Reduced demand charge Reduced peak electric energy costs

CHP systems can offer much higher energy efficiency than conventional standalone equipment items for similar degree of power reliability, comfort cooling, heating and indoor air quality. Because of the higher energy efficiency of the CHP system, it consumes nearly 40% less fuel than conventional systems. The reduced fuel consumption can significantly reduce energy costs. The cost of electricity to buildings is generally based on power demand (measured in kW) and electric energy usage (measured in kWh). The power demand charge is generally a monthly charge (£/kW) based on the peak/maximum power used during a month for a specified period, generally 15 minutes to 30 minutes. Power demand charge rates can vary with time-of-year. CHP systems reduce power demand in two ways: 1) By generating some of the power at site 2) By using thermal energy from power generation equipment, instead of electricity, for operating cooling, heating and/or humidity control equipment. The charge for electric energy usage generally varies with the time-of-year and the time-of-day. This charge is the highest during peak periods, generally from 9AM until 3PM, and the least during off-peak period, generally from midnight until 7AM. Therefore, primary reduction in electric energy cost savings for using CHP systems comes from avoiding purchase of electric energy during peak periods. Reduced life-cycle costs Even though the initial cost of CHP systems for buildings is higher than purchasing all electric power needs and using conventional chillers and boilers for cooling, humidity control and heating needs, the life-cycle cost of the CHP systems is often lower because of the energy cost savings over its useful life of more than 20 years.

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Steve Goddard

Attractive return on investment On an overall basis, CHP systems can reduce energy costs for buildings. If the incremental installed cost of CHP systems over conventional systems is treated as an investment, and the annual savings in its energy costs are treated as the return on that investment, the return can be very attractive. Improved environmental quality Integrated systems for CHP for buildings improve efficiency of energy utilization to as much as 85% compared to that of about 35% for conventional systems. Increased efficiency of energy utilization decreases the amount of fossil fuel consumed per unit of energy used and leads to 45% reduction in air emissions compared to conventional centralized power plants. Also of increasing interest, is the relationship of indoor air quality to our health. In order to prevent the growth of mold, mildew and bacteria, it is important to keep humidity in the indoor air to below 60%. CHP for buildings can help improve indoor air quality by supporting the use of a desiccant dehumidification system to dry the air. Desiccant systems use a material that directly removes the moisture from the air then use heat, such as that provided by the exhaust gases of the power generation equipment in the CHP system, to regenerate the desiccant. This provides a very energy efficient and cost effective method of dehumidifying indoor air, rather that using an air conditioner to "over cool" the air to remove humidity. Reduced energy consumption Integrated systems for CHP for buildings increase efficiency of energy utilization from 51% for conventional power generation systems to as much as 85%. Therefore, the use of these systems reduces the consumption of fossil fuels, for a unit of energy required for a building, by about 40% of that used by conventional systems. In other words, conventional systems require 65% more energy than the integrated systems, as shown in the diagram below. This is important for prolonging the period of availability of our scarce fossil fuel resources (natural gas, oil and coal) and reducing our dependence on imported fuel and on nuclear energy.

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Steve Goddard

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Steve Goddard

Q3.2 Produce a documented system analysis relating to the energy distribution A combined cycle gas turbine generator has a fuel input of 100%. The losses through the gas generator are 6%, loss in waste heat recovery is 2%, steam generator losses are 6% and stack losses are 11%. The electricity produced is equal to 40% and the low pressure steam provided for heating is 35%. Draw a sankey diagram to illustrate this.

Q3.3 Select and evaluate the appropriate cost saving technique for the chosen situation From the information stated in the scenario above (see front sheet) and by using a Sankey diagram show how the energy is lost through the building. Take the total losses as 100%. Identify the best means of saving energy against cost if each double glazed window were to cost £650, each double glazed door cost £1100, cavity wall insulation would cost £50 per cubic metre and fibre glass lost insulation were to cost £15 for a roll 10m long by 1m wide by 100mm thick. Rank the insulation techniques in order of their cost effectiveness. Firstly I worked out the total surface areas: Wall Surface Area

(2 x 100 x 2.5) + (2 x 40 x 2.5) =

700 m2

Roof Surface Area

40 x 100 =

4000 m2

Double Door Surface Area

(2 x 2) x 2 =

8 m2

Window Surface Area

(1.5 x 2) x 18 =

54 m2

Total Wall Surface Area – Windows and Doors

700 – 58

638 m2

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Steve Goddard Using the R values on the sheet we got given during lectures I worked out the total U value of the wall.

Brick – 100mm with an R value of 0.12 Air Cavity – 100mm with an R value of 0.18

Breeze Block – 200mm with an R value of 0.18 Plasterboard – 2.5mm with an R value of 0.03 The total R value is 0.51 therefore U = 1.96 Next I multiplied the U value by the surface area of the walls to show the total energy loss. 1.96 x 638 = 1250.5 W Energy Loss The single glazed doors have a U value of 5. 5 x 8 = 40 W Energy Loss The single glazed windows have a U value of 5. 5 x 54 = 270 W Energy Loss The Roof has a U value of 1.9. 1.9 x 4000 = 7600 W Energy Loss The total loss throughout the building is 9160.5 W. 13.65 % Lost through the walls 0.44 % Lost through the doors 2.95 % Lost through the windows 82.96% Lost through the roof

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Steve Goddard Double Glazed windows total cost = £11700 Double Glazed doors total cost = £2200 Cavity Wall insulation = £3190 Loft Insulation = £6000 for 400 roles Windows Double Glazing has a U value of 3 Energy Loss = 3 x 54 = 162 down from 270 Energy Saved = 108 W Doors Double Glazed doors have a U of 3 Energy Loss = 3 x 8 = 24 down from 40 Energy Saved = 16 W Roof Insulation K value of 0.035 = R value of 2.86 Tiled Roof with no felt = R value of 0.52 Total R value = 3.38 Therefore a U value of 0.3 0.3 x 4000 = 1200 W down from 7600 W Energy Saving of 6400 W Walls Brick has R value of 0.12 Insulation has R value of 5.26 Blocks have R value of 0.18 Plaster has R value of 0.03 Total = 5.59 Therefore a U value of 0.18 0.18 x 638 = 114.84 W down from 1250.5 Energy Saving of 1135.66 W Double Glazing Windows - £11700/108 = £108.30 cost per Watt saved. Double Glazing Doors - £2200/16 = £137.50 cost per watt saved. Roof Insulation - £6000/6400 = £0.93 cost per Watt saved Wall Insulation - £3190/1135.66 = £2.80 cost per Watt saved So overall ranking from best to worse, Roof insulation, Wall Insulation, Double Glazing Windows and finally Double Glazing Doors.

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Steve Goddard

Bibliography Class Notes University of Massachusetts - http://www.northeastchp.org/nac/CHP Typical Heat Transferences handout

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