Prepared by:-

Alan Twaddle

HNC Building Services Engineering

30th October 2008

Brief

You are working in a Building Services Consultants office and are tasked with the job of designing building services systems for domestic and commercial buildings.

You will use all available guidelines and legislation to complete working designs of an air conditioning system for a commercial building.

Consult relevant documents such as; CIBSE guides, Building Regulations, HVCA documents, European and British standards.

Your brief includes some preliminary data searches and compilation of relevant information.

The initial design will examine natural ventilation and the possibility of using it to save energy in the project building.

Design calculations will be carried out at the initial stages of the design to size plant and equipment and provide energy efficient services systems that meet all performance criteria for energy consumption.

The evaluation of heat gains is an important step in ascertaining whether or not air conditioning is required in a building. Your design should include details of air conditioning systems from information gathered from appropriate sources.

QUESTION NO. 1

QUESTION NO. 1

Ventilation and air conditioning needs

1. Produce a table of inside environmental design requirements for the Leisure Centre building.

Typical Internal Design Criteria - Leisure Centre Building

Room	Internal Temperatures Deg C	Relative Humidity	Ventilation Lts/person	Lighting Levels Lux	Noise Rating
Offices	Winter Summer 19 min Uncontrolled	Uncontrolled	12 - 24	300	NR35
Fitness Suite	16 min. 23	Uncontrolled	12 - 24	300	NR40
Foyer	18 min. Uncontrolled	Uncontrolled	N/A	200	NR40
Restaurant	19 min. Uncontrolled	Uncontrolled	12	150/300	NR40
Reception	19 min. Uncontrolled	Uncontrolled	12	150/300	NR40
Toilets	18 min. Uncontrolled	Uncontrolled	10ac/h Extract Only	200	NR45
Changing Areas (Dry)	20 min. Uncontrolled	Uncontrolled	10ac/h Extract 8ac/h Supply	200	NR45

To follow : - Typical Internal Design Criteria - Leisure Centre Building Other Areas if Applicable

Swimming Pool	29 min. 29 min. +- 1 +- 1	50-70 %	10l/s /m2	600	NR45
Changing Areas (Wet)	25 min. Uncontrolled	Uncontrolled	10ac/h Extract 8ac/h Supply	200	NR45

QUESTION NO. 2

QUESTION NO. 2

2. Determine, using a psychrometric chart, the heater battery and cooling coil outputs and the supply air temperature for the Activity Room in the Leisure Centre.

ROOM CONDITION DESIGN

16 deg. C , 50 % sat ( CIBSE Guide A Table 1.5 )

Outside Design Conditions

27 deg. C, 80% sat.

Ventilation rate = 10 AC/H ( CIBSE Guide A, table 1.5 )

Fresh air vent rate = 24 l/s/person x 30 persons = 720 l/s = 0.72 m3/s. volume flow rate

Mass flow rate = M = VxD = 0.72 x 1.2 = 0.864 Kg/s.

Fresh Air rate in AC/H = 0.72 x 3600 = 2592 m3/h

2592 / volume (21x18x4.5) = 2592 / 1701 = 1.52 AC/H

% fresh Air = 1.5 / 10 = 0.15 x 100 = 15% fresh Air.

Mix ratio = 15% fresh Air 85% recirc

Cooling Coil Output

The cooling coil output is as follows:

H _{cooling coil} = m_a (h_M - h_ADP)

where:
H _{cooling coil} = Cooling coil output (kW)
m_a = mass flow rate of air (kg/s)
h_M = specific enthalpy at condition M (kJ/kg) determined from psychrometric chart.
h_ADP = specific enthalpy at condition ADP (kJ/kg) determined from psychrometric chart

The specific enthalpies at points M and ADP are shown on the psychrometric Chart above.

H _{cooling coil} = 0.864 ( 37 - 19 )

H _{cooling coil} = 15.55 kW

Reheater Battery Output

The heater battery or reheater output is as follows:

H _{heater battery} = m_a ( h_S - h_W)

where:
H _{heater battery} = Heater battery output (kW)
m_a = mass flow rate of air (kg/s)
h_S = specific enthalpy at condition S (kJ/kg) determined from psychrometric chart.
h_W = specific enthalpy at condition W (kJ/kg) determined from psychrometric chart.

The specific enthalpies at points W and S are shown on the psychrometric Chart above.

H _{heater battery} = 0.864 ( 29 - 19 )

H _{heater battery} = 8.64 kW

Note calculation based on Summer time only i.e. cooling coil for summer conditions and reheater for summer conditions to remove moisture.

QUESTION NO. 3

3. Discuss the possibility of using mechanical ventilation instead of air conditioning in the Leisure Centre building.

Air Conditioning and Ventilation

Ventilating buildings is an important part of forming comfortable spaces for work and living. Enhanced building regulations have improved U-values but convective heat losses have increased. Energy consumption has risen significantly due to often unnecessary increase in the use of air conditioning in many buildings. It has also been realised how much energy can be lost as a result of uncontrolled air passing through leaky buildings. A vital part of improving building energy performance is getting the issues right at the design stage. Ventilation and air conditioning systems come in many types but whether natural, mechanical or a combination of the two, they need to have a good degree of local control and meet health, comfort and cooling needs. A crucial factor in energy efficiency is defining the optimum ventilation rate as conditions such as excessive fresh air will cause excessive energy consumption while an inadequate amount of fresh air will see a rapid decline in internal air quality. 5 litres/sec per person is the minimum required rate though the recommended rate is 10 litres/sec per person. An advised strategy is to avoid smoking in buildings or provide separately ventilated rooms for smokers as cigarette smoking can double or quadruple this requirement.

Air Conditioning - Build tight, ventilate right!

The greatest energy loss from buildings is often from ventilation though the importance of this has become more apparent as conduction losses have been reduced with improved levels of insulation. Therefore it is important that a tight envelope is developed from the design stage to minimise uncontrolled air infiltration. A common rule for both mechanical and naturally ventilated buildings is “Build tight, ventilate right”. To minimise air leakage and infiltration, attention to detailing and sealing is paramount. The common points of infiltration include gaps around the perimeter of doors and windows, the areas where door and window frames meet a wall and the junctions of walls, ceilings and floors. Often the blame lies with poor workmanship, especially in service ducts. Very large energy losses in existing buildings and some recently built buildings are often through uncontrolled ventilation and are worse than the minimum standards which are often easily achievable. Controlled ventilation is essential in tight buildings as they can have problems unique to them such as a total lack of ventilation can lead to mould growth and other similar problems.

A move to a mechanical ventilation or air conditioning system

If possible, it is advisable to use natural ventilation rather than instantly opting for Air Con solutions which rely on mechanical systems. Buildings that are naturally ventilated tend to use less energy than those with mechanical based ventilation and air conditioning. Driving force for air movement is generated by a stack effect which is achieved by using air passages at different heights and wind effects. This is often achieved by ventilating from at least two facades. Buildings that rely on natural ventilation generally provide advantages such as lower energy consumption leading to lower running costs, the transport energy associated with fans is reduced, the risk of possible plant noise

is reduced and capital and maintenance costs are reduced. High levels of noise or pollutants and other external environmental conditions which may limit or preclude natural ventilation usage need

to be identified at an early stage and minimised where it is possible. If windows have been kept shut to keep out noise, fumes, dirt or smoke, it may mean a move to a mechanical ventilation or air conditioning systems which will result in higher energy consumption. A most important factor in

successful natural ventilation strategies is the minimisation of internal heat gains. When trying to retain a natural ventilation solution, efficient lighting, office equipment and solar shading are all beneficial, with 40W/m2 generally regarded as excessive and subject to assessment previous to the selection of a ventilation strategy. The need for mechanical cooling can also be avoided by using night air to cool the building fabric. Incidentally, the building fabric can absorb the incidental gains during the occupied hours and act as a heat sink which can be used as a thermal store.

Many buildings have air conditioning installed simply as it is seen as the best solution or for the reason of higher rental value that comes with that. Mechanical ventilation and air conditioning are energy intensive processes and factors such as noise, pollution, excessive heat gains can prevent a passive solution meaning that designers need to consider the next best energy efficient means of providing ventilation. There are a range of mixed mode solutions that can provide intermediate options and involve a variety of ventilation and cooling systems. An example is to rely on ventilation and cooling by opening windows and turning off the air conditioning for parts of the season. Another example is zoning which works by keeping the bulk of the building naturally ventilated while massing all significant heat producing equipment into a space with the appropriate air conditioning.

Full Air Conditioning

When a full air conditioning system is added to a design it can add up to 50 percent to the total running costs for the building and therefore, should be very carefully considered. While full air conditioning involves humidity control, the UK term often refers to systems which simply provide cooling and heating, sometimes referred to as comfort cooling. If it is necessary to use air conditioning then one way to save energy is to avoid humidity control. Often there is little need for tight temperature control and the introduction of flexibility in the original design specification can lead to less energy use.

The fact that mechanical ventilation requires higher air change rates than those in naturally ventilated buildings leads to increased HV AC running and capital costs. One of the largest energy users in offices with air conditioning is air handling and this is often a much greater amount of energy use than chillers. The typical use if air handling in offices is 42-44kWh/m2/yr though best practice installations can roughly half that. Often, systems are over installed and greater than 12W/m2 is excessive while best practice is around 8W/m2. Therefore, sizing the fan is important as it needs to be as close to the real demand as possible to avoid unnecessary costs. The fan power which is a measure of the fans efficiency should be kept as low as possible. Good practice for offices is below 2W/litre/second and with very energy efficient systems; 1W/litre/second can be achieved. Anything above 4W/litre/second can be regarded as having a poor standard of efficiency and many existing systems are oversized with poor fan power. This can be prevented by matching equipment closely to demand and specifying high efficiency fans and motors.

Minimise energy consumed in air conditioning

Measures to minimise energy consumed in air conditioning are included in Building Regulations Part L2. This includes the necessary requirements for refurbished and new buildings as well as existing

buildings with an air conditioning or ventilation system is due to be altered or replaced. Showing that the Carbon Performance Rating (CPR) falls within certain limits is a way if achieving compliance in office environments.

Another way of achieving compliancy in offices is meeting ‘Whole Office’ CPR targets. Meeting specific fan power targets in other buildings requires 2W/litre/sec in new buildings, 3W/litre/sec in refurbishments while schools and hospitals comply by following DFEE and NHS guidelines.

QUESTION NO. 4

4. Discuss the possibility of using natural ventilation as a means of cooling the Fitness suites and Activity area of the Leisure Centre.

Design a suitable natural ventilation system for these areas.

Design for Natural Ventilation

The design of controlled natural ventilation systems requires identification of the prevailing wind direction, the strategic orientations and positions of openings on the building envelope. These openings include windows, doors, roof ventilators, skylights, vent shafts, and so forth.

Ventilation rates

When designing a ventilation system, the ventilation rates are required to determine the sizes of fans, openings, and air ducts. The methods that can be used to determine the ventilation rates include:

(a)  Maximum allowable concentration of contaminants

A decay equation can be used to describe the steady-state conditions of contaminant concentrations and ventilation rate, like this:

Ci = Co + F / Q

(3)

where	Ci	= maximum allowable concentration of contaminants
	Co	= concentration of contaminants in outdoor air
	F	= rate of generation of contaminants inside the occupied space (l/s)
	Q	= ventilation rate (l/s)

(b)  Heat generation

The ventilation rate required to remove heat from an occupied space is given by:

(4)

where	H	= heat generation inside the space (W)
	Q	= ventilation rate (l/s)
	cp	= specific heat capacity of air (J/kg.K)
		= density of air (kg/m^3)
	Ti	= indoor air temperature (K)
	To	= outdoor air temperature (K)

Air change rates

Most related professional institutes and authorities have set up recommended ventilation rates, expressed in air change per hour, for various situations. The ventilation rate is related to the air change rate by the following equation:

(5)

where	Q	= ventilation rate (l/s)
	V	= concentration of contaminants in outdoor air
	ACH	= air change per hour

Flow caused by wind

Major factors affecting ventilation wind forces include:

average wind speed;

prevailing wind direction;

seasonal and daily variation in wind speed and direction;

local obstructing objects, such as nearby buildings and trees;

position and characteristics of openings through which air flows; and

distribution of surface pressure coefficients for the wind.

Natural ventilation systems are often designed for wind speeds of half the average seasonal velocity because from climatic analysis there are very few places where wind speed falls below half the average velocity for many hours in a year.

The following equation shows the air flow rate through ventilation inlet opening forced by wind:

(6)

where	Q	= air flow rate (m^3/s)
	A	= free area of inlet openings (m^2)
	v	= wind velocity (m/s)
	Cv	= effectiveness of the openings (assumed to be 0.5 to 0.6 for perpendicular winds and 0.25 to 0.36 for diagonal winds)

Flow caused by thermal forces

If the building's internal resistance is not significant, the flow caused by stack effect may be estimated by:

(7)

where	Q	= air flow rate (m^3/s)
	K	= discharge coefficient for the opening (usually assumed to be 0.65)
	A	= free area of inlet openings (m^2)
	h	= height from lower opening (mid-point) to neutral pressure level (m)
	Ti	= indoor air temperature (K)
	To	= outdoor air temperature (K)

Guidelines for natural ventilation

The following guidelines are important for planning and designing natural ventilation systems in buildings:

a natural ventilation system should be effective regardless of wind direction and there must be adequate ventilation even when the wind does not blow from the prevailing direction;

inlet and outlet openings should not be obstructed by nearby objects;

windows should be located in opposing pressure zones since this usually will increase ventilation rate;

a certain vertical distance should be kept between openings for temperature to produce stack effect;

openings at the same level and near the ceiling should be avoided since much of the air flow may bypass the occupied zone;

architectural elements like wingwalls, parapets and overhangs may be used to promote air flow into the building;

topography, landscaping, and surrounding buildings should be used to redirect airflow and give maximum exposure to breezes;

in hot, humid climates, air velocities should be maximised in the occupied zones for bodily cooling;

to admit wind air flow, the long façade of the building and the door and window openings should be oriented with respect to the prevailing wind direction;

if possible, window openings should be accessible to and operable by occupants;

vertical shafts and open staircases may be used to increase and generate stack effect;

openings in the vicinity of the neutral pressure level may be reduced since they are less effective for thermally induced ventilation; if inlet and outlet openings are of nearly equal areas, a balanced and greater ventilation can be obtained.

Barriers to the application of natural ventilation

A successful application of natural ventilation strategies is only possible when there are no problems in many areas at various levels from the design stage to actual operating demands placed on the building users (Allard, 1998). These potential barriers include:

Barriers during building operations

Safety concerns

Noise from outdoor

Dust and air pollution

Solar shading covering the openings

Draught prevention

Knowledge of the users about how to take the best advantage of natural ventilation

Barriers during building design

Building and fire regulations

Need for acoustic protection

Difficult to predict pattern of use

Devices for shading, privacy & daylighting may hamper the free flow of air

Problems with automatic controls in openings

lack of suitable, reliable design tools

Other barriers

Impact on architectural & envelope design

Fluctuation of the indoor conditions

Design a naturally ventilated building requires more work but could reduce mechanical system (design fee on a fixed percentage of system's cost)

Increase risk for designers

Lack of suitable standards

Infiltration and Air Leakage

Infiltration is the uncontrolled flow of air through openings in the building envelope driven by pressure differences across the building shell. The surface pressure driving the air flow include:

- wind pressure;

- pressures arising from temperature difference between indoor and outdoor; and

- pressures resulting from operation of mechanical exhaust.

The infiltration rate of a building depends on weather conditions, equipment operation and occupant activities. The characteristics of infiltration air flow may be determined by measuring the air leakage of the building envelope which describes the relative tightness of a building. Typical leakage rates are around 6 to 10 air changes per hour at 50 Pa pressure difference.

Control of infiltration is needed to assure indoor thermal comfort and to minimise building energy use. Normally, infiltration may be lessened by reducing the surface pressures driving the air flow, for instance, through changing the landscaping in the vicinity of the building. A more common method is to reduce the air leakage of the building shell (for example, increase air tightness).

Air leakage area and performance

Air leakage is a measure of the air tightness of the building envelope. In practical building design, the air tightness of the whole building or its components is expressed as a leakage rate (in air change per hour), or an air leakage area.

Building air leakage area is a physical property of a building determined by its design, construction, seasonal effects, and deterioration over time. The larger the air leakage, the larger its infiltration rate. However, no simple relationship exists between a building’s air tightness and its air exchange rate, although some empirical methods have been developed to estimate the values.

The air leakage in buildings may be determined by pressurisation testing or tracer gas measurement. Ratings for air tightness have been established in some standards based on air flow rates predicted at particular reference pressures and test conditions. In some cases, the predicted air flow rate is converted to an equivalent or effective air leakage area using the following equation (which is derived from the Bernoulli equation for incompressible fluid flow):

(8)

where	AL	= effective air leakage area (cm^2)
	Qr	= predicted air flow rate at pr (m^3/s)
		= density of air (kg/m^3)
	pr	= reference pressure difference (Pa)
	CD	= discharge coefficient

For the whole-building case, all the openings in the building envelope are combined into an overall opening area and discharge coefficient for the building when the effective air leakage area is calculated. Therefore, the air leakage area of a building is the area of an orifice (with an assumed C_D value of 1 or 0.6) that would produce the same amount of leakage as the building envelope at the reference pressure.

The air leakage performance level for buildings is sometime presented as leakage classes (such as Class A, B, C and so on) and the appropriate classes are specified in building regulations based on climate. Table 3 shows the percentages distribution of air leakage for residential building components. It can be seen that the walls is the most important component, followed by ceiling details and heating system.

Table 3  Percentages of air leakage for residential building components

	Percentage of whole-building air leakage area
Components	Range	Mean
Walls	18 - 50%	35%
Ceiling details	3 - 30%	18%
Heating system (furnace, ducts)	3 - 28%	18%
Windows and doors	6 - 22%	15%
Fireplaces	0 - 30%	12%
Vents in conditioned spaces	2 - 12%	5%
Diffusion through walls	<1%

Estimation of infiltration rates

In the absence of any detailed information about the building, a simplified procedure may be used to roughly estimate the infiltration rates arising from both wind and stack effects. The degree of shielding and the building height are the factors taken into account in this method.

(9)

where	Ae	= effective leakage area (cm^2)
	Vr	= volume of the room (m^3)
	Q	= infiltrated air flow rate (m^3/h)
	Q/Ae	= specific infiltration (m^3/h.cm^2)

In this equation, the specific infiltration may be calculated by:

(10)

where	A	= stack coefficient (m^6/h^2/cm^4/K)
	B	= wind coefficient (m^6/h^2/cm^4/(m/s)^2)
	VW	= average wind speed at local weather station (m/s)
	T	= average indoor-outdoor temperature difference (^oC)

The values of stack coefficient and wind coefficient with respect to the different shielding levels are given in Table 4.

Table 4  Stack coefficient and wind coefficient

	Number of storeys
Description	One	Two	Three
Stack coefficient	0.00188	0.00376	0.00564
Wind coefficient
- no obstruction or local shielding	0.00413	0.00544	0.00640
- light shielding, few obstructions	0.00319	0.00421	0.00495
- moderate local shielding	0.00226	0.00299	0.00351
- heavy shielding	0.00135	0.00178	0.00209
- very heavy shielding	0.00041	0.00054	0.00063

Air leakage of building component

Additional test procedures for pressure-testing individual building components are also available. The component leakage data are useful to building design since they could be used to determine a more accurate picture of the likely air leakage performance. Table 5 shows effective air leakage areas for some building components. The values in the table give results in terms of air leakage area per unit component. Per unit component means per component, per unit surface area, or per unit length of crack or sash, whichever is appropriate. The air leakage areas may be converted to the results at other reference pressures, air flow rates, or flow coefficients using some empirical equations.

Table 5  Effective air leakage areas of building components

Building components	Unit	Best estimate	Range
Ceiling
- general	cm^2/m^2	1.8	0.79 - 2.8
- drop	cm^2/m^2	0.19	0.046 - 0.19
- recessed lights	cm^2/each	10	1.5 - 21
- surface-mounted lights	cm^2/each	0.82
Doors
- single, not weatherstripped	cm^2/each	21	12 - 53
- single, weatherstripped	cm^2/each	12	4 - 27
- double, not weatherstripped	cm^2/m^2	11	7 - 22
- double, weatherstripped	cm^2/m^2	8	3 - 23
- interior (stairs)	cm^2/lmc	0.9	0.25 - 1.5
- mail slot	cm^2/lmc	4
Walls (exterior)
- cast-in place concrete	cm^2/m^2	0.5	0.048 - 1.8
- clay brick cavity wall (finished)	cm^2/m^2	0.68	0.05 - 2.3
- precast concrete panel	cm^2/m^2	1.2	0.28 - 1.65
- low-density concrete block (unfinished)	cm^2/m^2	3.5	1.3 - 4
- low-density concrete block (painted)	cm^2/m^2	1.1	0.52 - 1.1
- high-density concrete blk. (unfinished)	cm^2/m^2	0.25
Windows
- awning, not weatherstripped	cm^2/m^2	1.6	0.8 - 2.4
- awning, weatherstripped	cm^2/m^2	0.8	0.4 - 1.2
- casement, not weatherstripped	cm^2/lmc	0.28
- casement, weatherstripped	cm^2/lmc	0.24	0.1 - 3
- double-hung, not weatherstripped	cm^2/lmc	2.5	0.86 - 6.1
- double-hung, weatherstripped	cm^2/lmc	0.65	0.2 - 1.9
- single-hung, weatherstripped	cm^2/lms	0.87	0.62 - 1.24
- single horizontal slider, weatherstripped	cm^2/lms	0.67	0.2 - 2.06
- single horizontal slider, wood	cm^2/lms	0.44	0.27 - 0.99
- single horizontal slider, aluminium	cm^2/lms	0.8	0.27 - 2.06
- storm inside, heat shrink	cm^2/lms	0.018	0.009 - 0.018
- window sill	cm^2/lmc	0.21	0.139 - 0.212
Electrical outlets/switches
- no gaskets	cm^2/each	2.5	0.5 - 6.2
- with gaskets	cm^2/each	0.15	0.08 - 3.5
Piping/plumbing/wiring penetrations
- uncaulked	cm^2/each	6	2 - 24
- caulked	cm^2/each	2	1 - 2
Vents
- bathroom with damper closed	cm^2/each	10	2.5 - 20
- bathroom with damper open	cm^2/each	20	6.1 - 22

Notes:	1.  lmc = linear metre of crack; lms = linear metre of sash.
	2.  Data based on a pressure difference of 4 Pa and CD = 1.
	3.  Data source: 1997 ASHRAE Fundamental Handbook, Chp. 25.

The building envelope of large commercial buildings are often thought to be quite air tight, but in fact many cases indicate that some components and the workmanship of them may affect the performance significantly. The infiltration calculations usually focus on doors and windows which are the obvious weak points. Lift, stair, service shaft walls; floors; and other internal partitions are also the major separating elements of concern in these buildings.

In large buildings, the air leakage associated with internal partitions is very important for evaluating internal air flow. Their leakage characteristics are needed to determine infiltration through exterior walls and air flow patterns within the building. These internal resistances are very essential for two aspects:

- in the event of a fire, to predict smoke movement patterns and determine smoke management strategies; and

- to support air movement calculations when designing air distribution systems.

NATURAL VENTILATION CALCULATION – FITNESS SUITE NO. 1

Q = C_d . A [ ( 2 / r_ins) r_ins . g . (h_npl – h ) (T_ins - T_out / T_ins ) ]

where;

Q = Air flow rate through a large opening (m³/s)

C_d = Discharge coefficient (0.61 for large openings)

A = Opening area (m²)

r_ins = Air density inside stack (kg/m³)

g = Acceleration due to gravity (9.81 m/s²)

h_npl = Height of neutral pressure level above datum (m)

h = Height of opening above datum (m)

T_out = Temperature of air outside stack (^oK)

T_ins = Temperature of air inside stack (^oK)

DATA

Assuming initial height of stack at 15 metres.

20 ACH/Hr for natural ventilation

Temperature inside stack 24 Deg.C, eins = 1.17 Kg/m3

Formula A = Area ( free Area ) required opening m2

DATA:

The flow rate required for the Fitness Suite is 20 air changes per hour.

The room measures internally 38 m x 17 m x 4m high.

The Fresh air louvre has a 50% free area.

Air flow rate for room Q = Room volume x Air change rate / 3600

Q = 39.4 x 21 x 4.5 x 20 / 3600

Q = 74,520 / 3600 = 20.7 m³/s

A = Q / cd ( ( 2 / eins ) eins x g x ( h npl –h ) x Tins – Tout / Tins )

A = 20.7 / 0.61 ( 1.17 x 1.17 x 9.81 x 9 x 0.167

A = 20.7 / 0.61 ( 29.5 )

A = 20.7 = 20.7

0.61 x 29.5 17.995

A = 1.15m2

Area at low level required = 1.15m2 free area.

To fit a louvre @ 50% free Area opening size = 1.15 x 2 = 2.3m2

Louvre size = 1.52m x 1.52m. at base of stack.

Comment

To provide a stack or chimney to provide this type of ventilation is of course very energy efficient

However restrictions on the build ( Architectural and other ) need to be discussed at a very early stage.

Effectiveness

The effectiveness of natural ventilation for commercial buildings depends on several criteria. These are wind strength and direction, size of openings, air temperatures and height of building. For effective controlled ventilation the designer should not rely solely on the wind but more on the stack effect and air controls.

Dampers can be used to control air entering and/or exiting a natural ventilation system. These dampers could be linked to occupancy sensors, temperature sensors, time switches and other weather sensors to give automatic control of ventilation which is the key to a useful system.

Cooling loads, energy requirements and peak

summertime temperatures

QUESTION NO. 5

5. Use the CIBSE guide to calculate solar irradiance on a vertical, horizontal and pitched surface of the Leisure building.

INTRODUCTION

Energy from the Sun reaching the Earth drives almost every known physical and biological cycle in the Earth system. By making solar radiation calculations and examining radiation measurements, students can gain a better understanding of many physical cycles and concepts associated with the Earth system.

A detailed study of solar irradiance will give Earth & Space Science and Physics students a better understanding of:

Solar radiation

Electromagnetic spectrum

Mathematical concepts that apply to solar radiation

Climate variation due to latitude

Seasonal weather changes

Global energy balance

Daily changes in solar radiation

Changes in solar irradiance due to solar cycles

Effects of solar irradiance variations on the earth system

This educational brief is designed to serve as a source of background information on solar radiation studies and as a reference for student investigations on this subject. Links to student investigations can be found at the end of this brief. Before beginning a detailed investigation of solar radiation, there are three terms that must be understood.

Irradiance - The amount of electromagnetic energy incident on a surface per unit time per unit area. In the past this quantity has often been referred to as "flux".
* When measuring solar irradiance (via satellite), scientists are measuring the amount of electromagnetic energy incident on a surface perpendicular to the incoming radiation at the top of the Earth's atmosphere, not the output at the solar surface.

Solar Constant - The solar constant is the amount of energy received at the top of the Earth's atmosphere on a surface oriented perpendicular to the Sun’s rays (at the mean distance of the Earth from the Sun). The generally accepted solar constant of 1368 W/m² is a satellite measured yearly average.

Insolation - In general, solar radiation is received at the Earth's surface. The rate at which direct solar radiation is incident upon a unit horizontal surface at any point on or above the surface of Earth. *I will refer to insolation as direct solar radiation at the Earth's surface.

The solar constant is an important value for current studies of global radiation balance & climate models. The problem that faces scientists studying Earth’s radiation budget and climate is that while satellites can “accurately” measure solar irradiance and calculate a solar constant, the surface insolation is much more difficult to assess. When the solar constant is calculated there are four major problems in trying to relate this radiation intensity to its effect on the Earth's surface or surface insolation.

First, the calculation is made for the top of the atmosphere and not for the surface of the Earth.

Second, the calculation assumes that the surface receiving the radiation is perpendicular to the radiation.

Third, the calculation assumes that the surface receiving the radiation is at a mean Sun-Earth distance.

Fourth, the calculation assumes that radiation emission from the Sun remains constant.

Trying to relate calculations made for the top of the atmosphere to the surface is a problem because up to 70% of incoming radiation can be blocked by the atmosphere and cloud cover. In attempts to create global energy budget models, scientists must insert estimations for the amount of energy actually reaching the surface.

Assuming that the surface receiving the radiation is perpendicular to the incoming radiation is a problem because this is a rare occasion even at tropical latitudes due to the rotation of the Earth (time of day), tilt of the Earth's axis in relation to the incoming solar radiation (season), and the latitude and orientation of the surface. All of these factors change the angle of the surface receiving the radiation, which changes the intensity of the energy received.

Assuming that the radiation emission of the Sun is constant is a problem because this value fluctuates with cycles in solar activity. NASA satellites have measured incoming radiation since 1978 and have recorded changes in solar irradiance. This data can be accessed on the internet from Goddard Space Flight Center.

SOLAR RADIATION AND THE ELECTROMAGNETIC SPECTRUM

The electromagnetic spectrum consists of the entire range of frequencies and wavelengths at which electromagnetic waves can travel. The electromagnetic spectrum organizes energy types by wavelength and frequency. The peak wavelength of radiation emitted from an object is dependent upon the temperature of the object and can be calculated using the Wien Displacement Law when the temperature of the object is known. (In astronomy these are solid objects such as stars and planets.)

Wien Displacement Law:

maximum = 2897 / T
maximum = The peak wavelength of energy in
micrometers
T = The temperature of the object radiating energy

Using this law, the peak wavelength of radiation emitted from an object is inversely proportional to the temperature of the object. The irradiance or radiation output of an object can be calculated using the Stefan-Boltzman Law when the temperature is known.

Stefan-Boltzman Law: E = T⁴

E = Surface Irradiance of the object
* = Emissivity of the object
= Stefan-Boltzman Constant (5.67x10^-8 W/m²K⁴ )

T = Temperature of the object

*Emissivity is the factor of how well a surface can absorb and emit energy. Emissivity numbers range from 0 to 1. Very black objects such as charcoal have an emissivity near 1 while shiny objects have an emissivity near 0.

The Wien Displacement & Stefan-Boltzman laws strictly apply only to black bodies. Black bodies are capable of absorbing and emitting radiation at all wavelengths. Because the Sun & Earth are not perfect black bodies, applying these laws to them only allows approximate values to be obtained. The fact that the Sun is not a perfect black body is especially important when studying solar cycles. The most significant variations in solar radiation during these cycles occur in the UV & X-Ray portions of the solar spectrum. In order to compare solar emissions to black body emissions at the same temperature go to the Solar Spectrum/Black Body Graph.

SOLAR RADIATION ENTERING THE EARTH SYSTEM

In order to study the effects of solar radiation on the Earth system, it is necessary to determine the amount of energy reaching the Earth's atmosphere & surface. Once the surface irradiance of the Sun is determined the amount of energy reaching the top of the Earth's atmosphere can be calculated using the Inverse Square Law. The average amount of energy received on a surface perpendicular to incoming radiation at the top of the atmosphere is the solar constant. (*While this calculation can lead to a better student understanding of the Inverse Square Law, the accepted value is a yearly average from NASA satellite measurements.)

Solar Radiation Striking the top of the Earth's Atmosphere

The Inverse Square Law is used to calculate the decrease in radiation intensity due to an increase in distance from the radiation source.

Inverse Square Law: I = E(4x R²)/(4x r²)

I = Irradiance at the surface of the outer sphere
E = Irradiance at the surface of the object (Sun)
4 x R² = surface area of the object
4 x r² = surface area of the outer sphere

In order to calculate the solar constant the following equation is used:

So = E(Sun) x (R(Sun) / r)²
So = Solar Constant
E= Surface Irradiance of the Sun
R= 6.96 x 10⁵ km = Radius of the Sun
r = 1.5 x 10⁸ km =Average Sun-Earth Distance

Insolation: Solar Radiation Striking the Surface

I = S cos Z

I= Insolation

S~ 1000 W/m² (Clear day solar insolation on a surface perpendicular to incoming solar radiation. This value actually varies greatly due to atmospheric variables.)

Z = Zenith Angle (Zenith Angle is the angle from the zenith (point directly overhead) to the Sun's position in the sky. The zenith angle is dependent upon latitude, solar declination angle, and time of day.)

Z = cos^-1 (sin sin + cos cos cos H)

= Latitude
H = = Hour Angle = 15^o x (Time - 12) (Angle of radiation due to time of day. Time is given in solar time as the hour of the day from midnight.)

= Solar Declination Angle

Solar Declination Angles for the Northern Hemisphere

Vernal Equinox Mar. 21/22 = 0^o
Summer Solstice Jun. 21/22 = +23.5^o
Autumnal Equinox Sept. 21/22 = 0^o
Winter Solstice Dec. 21/22 = -23.5^o

IRRADIANCE DATA SOURCES

In addition to making calculations for solar irradiation based upon physics concepts, students can access & analyze solar irradiance data that is collected by orbiting satellites and ground based pyranometers. Satellite irradiance data is available from 1978 to the present on the internet. The irradiance data has been collected by the following NASA satellites.

Nimbus 7 (Earth Radiation Budget) 1978- 1993
Solar Maximum Mission: Active Cavity Radiometer Irradiance Monitor I (ACRIM I) 1980-1989
Earth Radiation Budget Satellite (ERBS) Solar Monitor Measurements 1984- 1996
Upper Atmosphere Research Satellite (UARS) ACRIM II Measurements 1991-1997

Data and further information related to these satellites is available through the NASA Goddard Space Flight Center Data Archive Center.

SOLAR IRRADIANCE CALCULATIONS LEISURE CENTRE

Information from CIBSE Guide J (2002) Table 5.11 - Monthly Mean Daily Irradiation in Manchester (Aughton)

Includes Beam + Diffuse = Total Irradiation on 30^o inclined plane - South facing

Daily Irradiation from CIBSE guide
Month	Daily Irradiation (Wh/m^2)	Days per month	Monthly Irradiation (Wh/m^2)
January	1002	31	31,062
February	1732	28	48,496
March	2582	31	80,042
April	4051	30	121,530
May	5051	31	156,581
June	4868	30	146,040
July	4868	31	150,908
August	4117	31	127,627
September	3292	30	98,760
October	1994	31	61,814
November	1104	30	33,120
December	679	31	21,049
Total per year	-		1,076,633

SOLAR IRRADIANCE CALCULATION VERTICAL SURFACE

South facing wall Fitness Suite No. 1

25.0 x 9.2 = 230m2 x 2,544 x 365 = 2135,68800 Kilo watt hours.

SOLAR IRRADIANCE CALCULATION HORIZONTAL SURFACE

Ridge line of Fitness Suite No. 1

7.2m2 x 77,130 Wh/m2 = 555,336 Kilo watt hours.

SOLAR IRRADIANCE CALCULATION PITCHED SURFACE

South facing roof over Fitness Suite No. 1

Area = 48m2 x 30% = 62.4m2

62.4 m2 x 1,076,633 Wh/m2 = 671,81899.2 Kilo watt hours.

QUESTION NO. 6

6. Discuss a system of reducing solar cooling loads in the Leisure Centre building.

External window shading devices such as awnings, roof overhangs, shutters, and solar screens, and internal shading devices such as curtains and blinds, can control the entry of solar heat. However, shutters, solar screens, curtains, and blinds make rooms dark. Curtains and blinds also let in some of the undesirable heat. While exterior shading devices are about 50% more effective than internal devices at blocking solar heat, they may create problems with the building's aesthetics and are sometimes expensive to build. It is also impractical to construct roof overhangs to effectively shade east and west facing windows.

The following are the percentages of the radiant energy that different types of internal shading devices transmit, reflect, or absorb:

Roller Shades: up to 25%, 15-80%, 20-65%

Vertical Blinds: 0%, 23%, 77%

Venetian Blinds: 5%, 40-60%, 35-55%

The weak thermal characteristics of windows became a prime target for research and development in the attempt to control indoor temperatures of buildings. This led to the development of low-emissivity or "low-e," glass and films that control heat gain and loss, reduce glare, minimize fabric fading, provide privacy, and occasionally provide added security in wind, seismic, and other high-hazard zones. New construction and window replacement applications commonly use glazing with these coatings.

Some low-e coatings and solar control films reduce solar heat gain without impairing visible light transmission excessively. These include tinted glass and spectrally selective coatings, which transmit visible light while reflecting the long-wave infrared portion of sunlight. Many spectrally selective coatings also have some low-e properties as well. Modern window glazing falls into three categories: chemically or physically altered glass, coated glass or films, and multiple-layered assemblies with or without either of the first two items.

Chemically or Physically Altered Glass
Tinting is the oldest of all the modern window technologies and, under favorable conditions, can reduce solar heat gain during the cooling season by 25% to 55%. Tinted glass is made by alteration of the chemical properties of the glass. Both glass and plastic laminate may be tinted. The tints absorb a portion of the sunlight and solar heat before it can pass all the way through the window to the room. Tinted glazings reduce the latter by 25-55%. "Heat absorbing" tinted glass maximizes its absorption across some, or all, of the solar spectrum. Unfortunately, the absorbed energy often transfers by radiation and convection to the inside.

Spectrally selective tints reduce infrared light (heat) transmission while allowing relatively more visible light to pass through (compared to bronze- or gray-tinted glass). For buildings that use daylight for lighting, a spectrally selective window is a good choice. Spectrally selective glass also absorbs much of the ultraviolet (UV) portion of the solar spectrum. In a multi-paned window, they function best as the outermost sheet of glazing. Thermal performance is increased when combined with a low-e coating. Spectrally selective coatings often have a light blue or green tint.

Coatings and Films
Low-e and reflective coatings usually consist of a layer of metal a few molecules thick. The thickness and reflectivity of the metal layer (low-e coating) and the location of the glass it is attached to directly affects the amount of solar heat gain in the room. Most window manufacturers now use one or more layers of low-e coatings in their product lines.

Any low-e coating is roughly equivalent to adding an additional pane of glass to a window. Low-e coatings reduce long-wave radiation heat transfer by 5 to 10 times. The lower the emissivity value (a measure of the amount of heat transmission through the glazing), the better the material reduces the heat transfer from the inside to the outside. Most low-e coatings also slightly reduce the amount of visible light transmitted through the glazing relative to clear glass. Here are representative emissivity values for different types of glass:

Clear glass, uncoated: 0.84

Glass with single hard coat low-e: 0.15

Glass with single soft coat low-e: 0.10

A pyrolytic coating baked on at a high temperature constitutes a "hard coat" low-e coating. These are often made of a metallic oxide. One layer is about 1/10,000 the diameter of a human hair.

"Soft coat" low-e coatings are applied to the glass at lower temperatures and even thinner thicknesses than hard coatings. Both types of low-e coatings (within insulated glazing assemblies) are typically warranted for 10 to 50 years.

The only spectrally selective coatings now available are modified soft coat low-e coatings. The selective properties of the coatings are determined by modifying the coating's thickness and number of layers. A spectrally selective tinted glazing with a pyrolytic hard coat serves a similar purpose. These spectrally selective hard coats are currently under development.

"Aftermarket" films are available for application on existing windows. They are relatively easy to apply on glazing up 36 square inches (91.5 square centimeters). They are often applied to the glass with a water soluble adhesive. To reduce the possibility of bubbles and wrinkles on large windows, have the film installed professionally. Most films should be applied to the inside surface of the glass since they can be damaged easily by weather. If you plan to install the film yourself, be careful to select the appropriate film for your needs, and understand all directions before beginning. Plastic films generally last about 8 to 10 years before they start looking worn.

Performance Selection
The key measures of window performance are the U-Factor, Solar Heat Gain Coefficient, and Visible Transmittance. The air leakage rating (measure of the rate of air loss around a window under a specific pressure differential) is also important, but not addressed here.

The U-Factor is a measure of how easily heat travels through a material. The lower the value, the lower the amount of heat transfer through the window (from the interior to the exterior). Some manufacturers rate thermal performance using R-Factors. R-Factor is the inverse of the U-Factor, i.e., 1/U = R, 1/R = U. For example: a U-Factor of 0.25 is the same as an R-Factor of 4.0. The overall or "total" or "whole window" U-Factor of any window depends on the type of glazing, frame materials and size, glazing coatings, and type of gas (air, or inert argon or krypton) between the panes. Some typical U-Factor ranges for different window assemblies are:

Single glazed: 0.91 - 1.11

Double glazed: 0.43 - 0.57

Triple glazed: 0.15 - 0.33

The Solar Heat Gain Coefficient (SHGC) is the fraction of solar heat that enters the window and becomes heat. This includes both directly transmitted and absorbed solar radiation. The lower the SHGC, the less solar heat that the window transmits through the glazing from the exterior to the interior, and the greater its shading ability. In general, South facing windows in houses designed for passive solar heating (with a roof overhang to shade them in the summer) should have windows with high a SHGC to allow in beneficial solar heat gain in the winter. East or West facing windows that get a lot of undesirable sun in mornings and afternoons, and windows in houses in hot climates, should have lower SHGC assemblies.

The visible transmittance (VT) refers to the percentage of the visible spectrum (380-720 nanometers) that is transmitted through the glazing. When daylight in a space is desirable, as in showrooms and studios, high VT glazing is a logical choice. However, low VT glazing such as bronze, gray, or reflective-film windows are more logical for office buildings or where reducing interior glare is desirable. A typical clear, single-pane window has a VT of 0.90, meaning it admits 90% of the visible light.

The ratio between SHGC and VT is called the light-to-solar gain ratio (LSG.) This provides a gauge of the relative efficiency of different glass types in transmitting daylight while blocking heat gains. The higher the ratio number the brighter the room is without adding excessive amounts of heat.

Here are typical values for the Total Window and Center of Glass ( ) for different types of windows:

Window and Glazing Types	SHG	VT	LSG
Single-glazed, clear	0.79 (0.86)	0.69 (0.90)	0.87 (1.04)
Double-glazed, clear	0.58 (0.76)	0.57 (0.81)	0.98 (1.07)
Double-glazed, bronze	0.48 (0.62)	0.43 (0.61)	0.89 (0.98)
Double-glazed, spectrally selective	0.31 (0.41)	0.51 (0.72)	1.65 (1.75)
ouble-glazed, spectrally selective	0.26 (0.32)	0.31 (0.44)	1.19 (1.38)
Triple-glazed, new low-e	0.37 (0.49)	0.48 (0.68)	1.29 (1.39)

Factors to consider when choosing windows are: climate, building design, building orientation, and external shading. Check with manufacturers for product specifications.

Calculating Energy Savings

Energy savings from solar control glazing are difficult to accurately predict. Predictions of savings are based on many variables such as: size and orientation of the windows, solar heat gain coefficient (SHGC), and the cooling load factor (CLF; the ratio of actual total cooling compared with total steady-state cooling during the same period at constant ambient conditions.) To make this somewhat simpler, some references combine these variables into one figure: the Heat Transfer

Multiplier (HTM). The HTM will vary with location, seasonal changes, time of day, shading, orientation, temperature, and building color.
There are also computer programs for sizing of heating/cooling systems. These can also be used to estimate solar heat gain from different types of windows (given the SHGC and climate). Typically, you run the same program for each choice in window type and find the dollar value of the difference in energy saved between the choices. You can then divide the purchase price by the estimated savings to determine simple payback.

Some solar control films are very costly and may have very long payback periods. In such cases it may make better sense to consider other shading devices such as awnings, overhangs, solar screens, shutters, roller shades, blinds, and draperies.

QUESTION NO. 7

7. Determine the total heat gain for the Activity Area in the Leisure Centre building.

Tabulate the data and draw conclusions from the data.

Compare the total heat gain using manual calculations with using Hevacomp software.

Heat Gain Calculations

HEAT GAIN CALCULATION FOR ACTIVITY ROOM

Section 1- Window Sensible Heat Gain

Qg = Ag Ug ( to – tr )

Qg = 219 x 2.0 x ( 27 – 21 )

Qg = 219 x 2.0 x 6

Qg = 2628 watts = 2.628 kW

Where;

Qg = Sensible heat gain through glass (W)

Ag = Surface area of glass (m2)

Ug = 'U' value for glass (W/m2 oC) (see CIBSE guide A (2006) Table 3.23 to 3.32).

to = outside air temperature (oC). Can be obtained from CIBSE Guide J (2002) - Tables

5.36 to 5.38 for various months and times in the day.

tr = room air temperature (oC)

Section 2- Solar Glass Gain

Qsg = Fc Fs qsg Ag

= 0.91 x 0.54 x 314 x 219

= 33,791 watts = 33.8 kW

where Qsg = Actual cooling load (W)

qsg = Tabulated cooling load from CIBSE Guide A (2006) Table 5.19 to 5.24 (W/m²)

F_c = Air node correction factor from CIBSE Guide A (2006) Table 5.19 to 5.24 or see Table below.

F_s = Shading factor from CIBSE Guide A (2006) Table 5.19 to 5.24 or see Table below.

A_g = Area of glass (m2)

The Air point control factors (F_c) and Shading factors (F_s) are given in the Table below for various types of glass, building weights and for open and closed blinds.

Air node correction factors (Fc)
	Building Weight	Single Glazing		Double glazing
		Horizontal blind		Horizontal blind
	Light	0.91		0.91
	Heavy	0.83		0.90
Shading factors (Fs)
Type of glass	Building Weight	Single Glazing		Double glazing
		Open horizontal blind	Closed horizontal blind	Open horizontal blind	Closed horizontal blind
Clear 6mm	Light	1.00	0.77	0.95	0.74
	Heavy	0.97	0.77	0.94	0.76
Bronze tinted 6mm	Light	0.86	0.77	0.66	0.55
	Heavy	0.85	0.77	0.66	0.57
Bronze tinted 10mm	Light	0.78	0.73	0.54	0.47
	Heavy	0.77	0.73	0.53	0.48
Reflecting	Light	0.64	0.57	0.48	0.41
	Heavy	0.62	0.57	0.47	0.41

Section 3- Infiltration Gain

Qsi = N V ( to – tr ) / 3

Qsi = 0.75 x 21 x 18 x 4.5 ( 27 – 21 ) / 3

Qsi = 2551.5 watts = 2.55kW

where Qsi = Sensible heat gain (W)

n = number of air changes per hour (h-1) (see note below)

V = volume of room (m3)

to = outside air temperature (oC) Can be obtained from CIBSE Guide J (2002) - Tables 5.36 to 5.38 for various months and times in the day.

tr = room air temperature (oC)

Infiltration gains should be added to the room heat gains.

Recommended infiltration rates are 1/2 air change per hour for most air-conditioning cases or 1/4 air change per hour for double glazing or if special measures have been taken to prevent infiltration.

We have used ¾ air change for this case.

Ventilation or fresh air supply loads can be added to either the room or central plant loads but should only be accounted for once.

Section 4- Internal Gains

Occupants = 30 people x 210 watts / persons = 6300 watts

Lighting = Compact florescent

= 500 Lux = 14 w/m2 x 21 x 18

= 5292 watts = 5.292 Kw

Machinery = 30 No. rowing machines @ 100 watts each

= 3000 watts = 3.0Kw

Sub Total = 14.592

Heat Gain from internal walls for the Activity Room only The South, east and West walls will

Have any significant heat gain.

The heat flow through a wall is complicated by the presence of thermal capacity, so that some of the heat passing through it is stored, being released at a later time similar to the use of storage heaters storing heat via economy seven tariff at night into concrete pattern blocks for releasing heat during the day.

Thick heavy walls with a high thermal capacity will damp temperature swings considerably, whereas thin light walls with a small thermal capacity will have little damping effect, and fluctuations in outside surface temperature will be apparent almost immediately.

The thermal capacity will not affect the daily mean solar gain but will affect the solar gain at a particular time.

The particular time q of a solar gain is normally the time of the maximum gain.

The heat gain arrives at the inside of a thick wall some time after the sun hits the outside surface of the wall.

This time lag is f.

The calculation is, therefore, again split into two components.

1. Mean gain through wall,

Q_q = A . U ( t_em - t_r)

where, Q_q = heat gain through wall at time q

A = area of wall (m²)

U = overall thermal transmittance (W/m² oC) (see CIBSE guide A (2006) Table 3.49 to 3.55) for typical wall constructions.

tem = 24 hour mean sol-air temperature (oC) CIBSE Guide J (2002) - Table 5.36 to 5.38.

tr = constant dry resultant temperature (oC). In practice room dry bulb is used.

2. The variation from the mean solar gain is subject to both a decrement factor and time lag.

Q_f = f ( t_eo - t_em)

where Qf = Heat gain through wall at time (q - f)

f = time lag in hours (see CIBSE guide A (2006) Table 3.49 to 3.55) for typical wall constructions.

teo = sol-air temperature at time (q - f) (oC) CIBSE Guide J (2002) - Table 5.36 to 5.38.

tem = 24 hour mean sol-air temperature (oC) CIBSE Guide J (2002) - Table 5.36 t 5.38.

f = decrement factor (see CIBSE guide A (2006) Table 3.49 to 3.55) for typical wall constructions.

Therefore the Solar Gain through a wall at time ( q - f) is;

Q_q+f = A . U ( t_em - t_r) + f ( t_eo -