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					                                                  BE326 Energy Assessment




s
School of the Environment


Semester 1 Examinations 2005-2006



BE326
ENERGY ASSESSMENT




Instructions to Candidates:

Time allowed: TWO hours

Attempt any FOUR questions




                              Wednesday 25 January 2006 9:00 – 11:00 hours




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                                                        BE326 Energy Assessment




Question 1

The role of an energy manager is to monitor energy consumption within a
building and to instigate measures that would increase efficiency and reduce
costs.

If you were the newly appointed energy manager for a 20,000 m 2 office building
situated in Brighton:

a)    Describe the procedures you would adopt in order to evaluate the current
      energy efficiency of the building and determine the most appropriate
      means of reducing consumption.                               (15 marks)

b)    The Building Regulations Approved Document L2 identifies the need for a
      Building Log Book. Identify the content of such a log book and discuss its
      relevance to optimizing energy consumption in the building.
                                                                   (10 marks)

Question 2

(a)   Degree days are a powerful tool in the evaluation of space heating energy
      consumption in buildings. Identify the basis for using 15.5oC as the base
      temperature for determining degree days in the UK and identify the
      limitations of using this base temperature.
                                                                   (5 marks)

(b)   The following degree day versus energy consumption graphs have been
      plotted for different buildings. They include different energy sources, not
      all of which will be related to space heating.

      Analyse each of the graphs and comment on the use of energy for each
      building. (All graphs show the origin as zero energy consumption, zero
      degree days).
                                                            (4 marks each)

      (i)
                 Energy Consumption




                                                                         Page 2 of 7

                                        Degree days
                                                         BE326 Energy Assessment


(ii)




        Energy Consumption




                                           Degree days
(iii)
                      Energy Consumption




                                           Degree days
(iv)
                      Energy Consumption




                                           Degree days
                                                                         Page 3 of 7
                                                       BE326 Energy Assessment


(v)




             Energy Consumption




                                   Degree days
Question 3

(a)   In order to be able to manage energy efficiently within buildings it is
      necessary to be able to monitor the consumption for different types of
      load. Discuss the need for the development of a clear metering strategy
      within a building. Illustrate your answer with the description of how you
      would develop an appropriate strategy for a presitigious new office
      building housing offices with facilities for a computer on every desk,
      restaurant, gymnasium and meeting rooms.                        (10 marks)

(b)   The owners of a small office building are considering upgrading the
      lighting system as an energy conservation measure. They are considering
      replacing the tungsten filament lamps with compact fluorescent lamps and
      need to estimate the overall advantages.

      Estimate the simple payback period anticipated for this replacement and
      the overall savings in carbon dioxide emissions, taking into account both
      the saving in lighting consumption and the increase in heating load.
                                                                       (15 marks)
      Data:
      Existing lighting load (tungsten filament)                3000W
      Proposed lighting load (compact fluorescent)              600W
      Cost of replacement lamps                                 £250
      Cost of electricity                                       7.5p/kWh
      Cost of gas                                               3.0p/kWh
      Electricity CO2 emission                                  0.5 kg / kWh
      Gas CO2 emission                                          0.2 kg / kWh
      Lighting Hours                                            1500 hrs /year
      Current Space Heating Load                                28,000 kWh /year

      The space heating is provided by a gas fired boiler operating at a
      seasonal efficiency of 70%.


                                                                           Page 4 of 7
                                                             BE326 Energy Assessment




Question 4

a)         A new dwelling is to be built near the seafront of Brighton. Use the data
           given below to calculate the:
            peak demand for space heating;
            annual space heating energy consumption; and
            hot water energy consumption.

     Data:

                                       U value [Wm-2K]        Area [m2]
     Wall (excluding windows)                 0.35              200
     Roof                                     0.25               90
     Windows                                   2.1               25
     Floor                                     0.4               90

     Design environmental temperatures: indoor 21°C, outdoor -1°C
     Ventilation rate: one air change per hour
     Volume of house: 160 m3
     Number of occupants: family of 2 adults and 3 children
     Average daily hot water consumption: 70 l/person
     Efficiency of hot water system is 85%
     Hot water supply temperature: 65°C
     Average incoming cold water temperature: 10°C
     Specific heat capacity of water 4200J/kgK
     Heating season: October to March

                                 Degree days for Brighton
     Jan     Feb   Mar   April   May     June   July   Aug   Sept   Oct   Nov   Dec
     360     331   293   231     146      74     36     42    79    160   265   321

                                                                            (15 marks)

b)         Identify the key elements that are included in the Standard Assessment
           Procedure (SAP) to establish the annual energy consumption of a
           domestic building.
                                                                        (10 marks)




                                                                             Page 5 of 7
                                                              BE326 Energy Assessment




Question 5
a)    Use the data given below to calculate the sensible cooling load for a
      south-facing office on the top floor of a building at three o’clock in the
      afternoon.
                                                                           (18 marks)

b)    Briefly describe the measures that can be considered to reduce the
      summer cooling load of an air-conditioned office building.
                                                                      (7 marks)
Data:
    Dimension of room 6m deep x 10m wide x 3m high
    Design dry resultant temperature is 21°C
    6 occupants each has a sensible heat emission of 100W
    Lighting and other equipment sensible heat gain is 1.5 kW
    Fresh air and infiltration rate is 0.6 air change per hour
    Solar radiation normal to the window glass at 15:00 is 360W/m2
                     Area        U value         Time lag       Decrement factor
                     (m2)        (W/mK)           (hours)
     Roof             60          0.20               1                0.8
     Wall             10          0.35               9                0.4
     Window           20           2.8               0                 1
     Shading coefficient of windows = 0.5

                                      Sol air temperature (°C)
      Hour   0000   0100     0200    0300     0400 0500 0600 0700            0800    0900    1000
      Roof    12     11       10       9.5     9.0     9    12.5 18.5        25.5     32      38
      Wall    14     13       12      11.5      11    11    15.5  22          29      35      39

      Hour 1100 1200        1300 1400         1500 1600 1700 1800            1900    2000    2100
      Roof 42.5 44.5        45      43        39    33.5 27.5 21.5           17.5    16.5    15.5
      Wall 41.5       42     39.5    35.5     30.5 24.5 21.5 19.5            18.5    17.5    16.5
      Mean sol-air temperatures for wall is 23°C, and for roof is 23.5°C

                                    Air temperature (°C) at
      0900   1000   1100    1200     1300 1400 1500 1600           1700     1800    1900
      14.5   16     17.5    18.5     20     21     21.5 21.5       21.5     21      20.5

      Mean air temperature = 16°C
      Density of air = 1.2 kg/m3
      Specific sensible heat capacity of air = 1.012 kJ/kgK




                                                                               Page 6 of 7
                                                       BE326 Energy Assessment




Question 6

The EU Directive on Energy Performance of Buildings has a significant impact to
the energy awareness and investments in buildings.

a)   Describe the objectives and methodology of this directive.
                                                                       (8 marks)

b)   Discuss the measures that will affect the design and operation of new and
     existing buildings.
                                                                       (17 marks)




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