Module: BENV0151 Energy and Environmental Systems Fundamentals Sustainable Built Environments, Energy and Resources BSc/MEng

SECTION A: CORE ASSESSMENT DETAILS

SECTION B: COURSEWORK INFORMATION

Coursework Brief:

For this coursework, you are requested to solve 5 problems  that  involve  applying  the developed knowledge into practice, focusing on the balance between energy demand and generation in (building) systems [Module Learning Objective #3]. The problems are set at different scales, ranging from simple architectural and service elements to whole buildings, so you will have to identify the corresponding challenges to meet specific energy and environmental performances [Module Learning Objective #2]. For each problem, you will be asked to include a brief discussion section, where you will have the opportunity to express your understanding of the interaction at play in each problem between the building/element, the “human factor”, and the context [Module Learning Objective #1].

For each of the problems listed, please develop your response using the following seven-step problem-solving approach.  Each  “step”  should be a corresponding  sub-heading of your response to all the 5 problems to solve.

The use of calculators or spreadsheets is allowed for this coursework.

Step 1: Problem Statement

In your own words, briefly state the problem, the key information given, and the quantities to be found. This is to make sure that you understand the problem and the objectives before you attempt to solve the problem.

Step 2: Schematic

Draw a sketch of the physical system involved and list the relevant information on the figure. The sketch does not have to be something elaborate, but it should resemble the actual system and show the key features (you can either use a graphic editor to generate it, or sketch it by hand, scan it, and copy-paste it into the document). Indicate any energy and mass interactions with the surroundings. Listing the given information on the sketch helps one to see the entire problem at once.

Step 3: Assumptions and Approximations

State any appropriate assumptions and approximations  made to simplify the  problem to make  it  possible to obtain a solution. Justify the questionable assumptions.  Assume reasonable values for missing quantities that are necessary.

Step 4: Physical Laws

Apply all the relevant basic physical laws and principles and reduce them to their simplest form by utilizing the assumptions made.

Step 5: Properties

Determine the unknown properties necessary to solve the problem from property relations or  tables.  List  the  properties  separately,  and  indicate  their  source  (i.e.,  references  in  a bibliography section), if applicable.

Step 6: Calculations

Substitute the known quantities into the simplified relations and perform. the calculations to determine the unknowns. Pay particular attention to the units and unit cancellations and remember that a dimensional quantity without a unit is meaningless. Also, don’t give a false implication of high precision by copying all the digits from the calculator—round the results to an appropriate number of significant digits.

Step 7: Reasoning, Verification, and Discussion

Check to make sure that the results obtained are reasonable and  intuitive and verify the validity of the assumptions. This is your chance discuss your understanding of the interaction at play in the given problem between the building/element, the “human factor”, and the context. This section may include references to literature, which you can report in the Bibliography.

The coursework should include a general Bibliography section at the end of the document (Harvard style. for references is required for cited literature), covering all sources used in the compilation of this coursework (e.g.,   tables  for  values/coefficients,  scientific   papers mentioned in the different discussion sections of each problem, etc.).

***PROBLEMS TO BE SOLVED***

Problem #1

A warehouse in London has a floor area of 200 m2 and an average height of 5 m.  The mechanical ventilation system guarantees a ventilation rate of 0.36 ACH. Determine the heat transfer rate associated with ventilation, knowing that there is a 10-degree Celsius difference between the temperatures inside and outside of the warehouse.  Assuming  that  the ventilation system is in operation for  10  hours a day, and that the heat loss needs to be compensated for by means of an electric heater, determine its weekly cost if the electricity price in that area is £0.061/kWh.

Discuss:

•   What  kind  of  activities  and  occupancy  level  would   be  acceptable  for  the  given ventilation rate? Why?

•   What are the sustainability implications of compensating heat losses via the proposed approach?

Problem #2

Consider a 3-m-high, 6-m-wide, and 0.3-m-thick wall made of exposed bricks. On a certain day, the temperatures of the inner and the outer surfaces of the wall are measured to be 16°C and 2°C, respectively. Determine the rate of heat loss through the wall on that day.

After that, assume you apply on the bricks wall a 10-cm-thick layer of rock wool insulation and a 2-cm-thick layer of plaster: these two materials have a thermal conductivity of λ = 0.05 and λ = 0.4, respectively. Determine the U-value (air-to-air) for this newly built multi-layer wall and the new rate of heat loss through the wall under the same temperature conditions. Discuss:

•   After applying the new materials, is the performance of the wall under consideration adequate for a residential building in England? Why?

•    How is sustainability related to adequate insulation in buildings? How does insulation impact energy consumption in buildings?

Problem #3

A fixed aluminium-framed window with glass glazing is being considered for an opening that is 1.2 m high and 1.8 m wide in the wall of a house that is maintained at 22°C. Determine the rate of heat loss through the window when the outdoor air temperature is 10°C, if the window is selected to be: (a) 3-mm single glazing, or (b) double glazing with an airspace of 12 mm.

Assuming now that outdoor there is a wind speed of 3 m/s, and the consequent convective heat transfer  rate  is  160  W,  determine  the  surface  temperature  of  the  external  glazing, knowing that the outdoor temperature of (undisturbed) air is still 10°C.

Discuss:

•    How are the two glazing scenarios different in terms of performance?

•    How do such different glazing options impact sustainability,  by considering energy efficiency and occupants’ comfort?

•   What are the implications for thermal bridges if a material other than aluminium was selected for the window frame?

The dimensions of a concrete wall of a building located in Rome (Italy) are 5*4 m. It has a surface temperature of 24°C. Calculate the radiative heat transfer from the wall to the outdoor environment in a typical day of January. Furthermore, knowing that the building is a rectangular prism with four such walls with a U-value of 2.0 W/m²·K, that the building has a square  floor  plan  of 25 m2,  and  floor  and  roof  have  U-values of 1.0 and 0.7 W/m²·K respectively, then calculate an approximation of the buiIding’s heat transfer coefficient.

Discuss:

•    How would the radiative heat transfer value change if a typical day in April was taken as a reference, instead of January?

•    For  radiative  heat transfer,  discuss the  implications of using materials other than concrete in world regions with different climates 一 include a city of your choice (e.g., your hometown, or a city you would like to visit) as an example.

Problem #5

A UCL cafeteria (V = 400 m3) that normally hosts 35 students from the SBEER Programme during their breaks is to be air-conditioned with window air-conditioning units of 5 kW cooling capacity each. A student at rest may be assumed to dissipate heat at a rate of 360 kJ/h. The lighting system in the room consists of 20 lightbulbs, each providing a radiative heat transfer of 100 W. The rate of heat transfer to the classroom through the walls and the windows on a summer day is estimated to be 15,000 kJ/h. If the room air is to be maintained at a constant temperature of 21°C, determine the minimum number of window air-conditioning units required.

Discuss:

•    Assuming the classroom had extra seats capacity, how would the increasing number of students affect the need for additional air-conditioning units?

•    What is the impact on sustainability of the need for additional air-conditioning units, under different configurations of energy supply from the grid?

•    Based  on the  content you  have been taught in the lighting session, consider how different types of bulbs may achieve similar brightness in lumens.

•    Considering that an average reverberation time of 0.5 s has been measured in the cafeteria, discuss what residual acoustical capacity the space may still have and how this could be increased.