Climate & Sensible Heat

PAUL HAY Capital Projects

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Sensible Heat & Climate

Author:          Paul Hay

e-mail:            paul.hay@phcjam.com

profile:           www.linkedin.com/in/phcjam

1.0   INTRODUCTION TO HEAT TRANSFER           

1.1_      The first law of thermodynamics states that energy cannot be created or destroyed, only transferred from one place to another, in one form or another.

1.2     Heat is energy transferred from one body to another as the result of a temperature difference between them:

1.2.1   Sensible Heat is heat energy that can be measured by a thermometer;

1.2.2   Latent Heat is stored energy that cannot be directly measured by a thermometer.

1.3       Heat transfer takes place in four different modes:

1.3.1   Radiation is the transfer of heat by electromagnetic waves which does not affect the medium through which it passes;

1.3.2   Convection is the transfer of heat through a fluid medium;

1.3.3   Conduction is the transfer of heat from one solid body to another through physical contact;

1.3.4   Phase Change is the transfer of heat which takes place when the medium undergoes a change of state.

2.0 SOLAR RADIATION INCIDENT ON THE EARTH VARIES

2.1       Solar Radiation is the short-wave heat input emitted from the sun;

2.2       Extra-terrestrial Radiation is solar radiation outside the Earth's atmosphere;

2.3       The intensity of extra-terrestrial radiation is constant over time;

2.4     The intensity of solar radiation incident on the Earth's surface varies during the course of a day because of  atmospheric attenuation and rotation of the Earth.

3.0   THE EARTH ROTATES ABOUT A SKEWED AXIS

3.1       The Earth's atmosphere is classified by temperature distribution into five layers:

3.1.1   The upper atmosphere comprises two cold layers having 90% of the Earth=s ozone layer.

3.1.2   A large portion of ultra-violet rays is removed by the ozone layer, thus changing the solar spectrum.

3.1.3   The lower atmosphere comprises three warm layers which represents 86% of the atmosphere by mass:

3.1.1   Clouds reflect 28% of solar radiation out of the lower atmosphere;

3.1.2   The atmosphere absorbs 25% of solar radiation;

3.1.3   Remaining Solar Radiation is separated into beam and diffuse components as it passes through the lower atmosphere.

3.2       Rotation of the Earth causes the angle of incidence with the surface to vary throughout the day.

3.3    Rotation of the Earth also causes attenuation to increase at sunrise and sunset because the path through the atmosphere is increased;

3.4       The Earth's surface absorbs 47% of the solar radiation;

3.5       The Cosine Law states that the intensity of an electromagnetic wave (such as solar radiation) on any surface is proportional to the cosine of the angle of incidence to the normal of the surface:

3.5.1   Higher latitudes receive less intense solar radiation;

3.5.2   Solar radiation is least intense at sunrise and sunset;

3.5.3   Solar radiation is more intense at noon; and

3.5.4   Solar radiation is most intense when the Sun's rays are perpendicular to the Earth's surface.

3.6       Ground cover shades or reflects a portion of the available solar radiation.

3.7       Thermal storage is primarily influenced by the oceans, which cover 75% of the Earth's surface.

4.0 TERRESTRIAL RADIATION IS RESPONSIBLE FOR COOLING

4.1       Terrestrial Radiation is the long wave heat output emitted from the Earth.

4.2       Atmospheric Turbidity inhibits transmission of terrestrial radiation.

4.3       Accumulation of carbon dioxide in the atmosphere also inhibits terrestrial radiation and is referred to as the AGreen House Effect@.

5.0 TEMPERATURE FLUCTUATES ACCORDING TO INCIDENT SOLAR RADIATION, TERRESTRIAL RADIATION AND THERMAL STORAGE BY EARTH

5.1       The temperature of the Earth's surface rises as solar radiation is absorbed:

5.1.1   Higher latitudes are colder when sunlight hours are reduced, because the intensity of  solar radiation is less;

5.1.2   Temperature increase is less over bodies of water because the heat capacity of water is 2-3 times higher than that of dry soil.

5.1.3   Heat Capacity is the ability of a given volume of material to store or absorb heat while undergoing a temperature change.

V = ρ x C_v                                                                                                             5.1

where.

V =  Heat Capacity, W/m³*K

ρ  =  Density, Kg/m³

C_v = Specific Heat, W/Kg*K

5.2       The Earth's surface transmits heat to adjoining materials:

5.2.1   A portion of heat at the surface of dry soil is conducted to deeper layers of soil;

5.2.2   A portion of heat at the surface of bodies of water is convected to greater depths;

5.2.3   Adjacent air is heated by conduction; and

5.2.4   Air currents transfer heat by convection.

5.3       Diurnal temperature results from daily storage of absorbed solar radiation and cooling by terrestrial radiation:

5.3.1   The amplitude of temperature fluctuations is greater over continental land masses;

5.3.2   The time lag of diurnal temperature is more delayed over continental land masses.

6.0   WIND RESULTS FROM DIFFERENTIAL HEATING ON THE EARTH'S SURFACE AND ROTATION OF THE EARTH

6.1       Differential heating gives rise to convective air-currents:

6.1.1   Land and Sea Breezes result from differential heating of land and sea;

6.1.2   Between latitude 30EN and 30ES, two opposite eddy currents develop, known as Hadley Cells.

6.2       The Earth's rotation sets up a Coriolis Force to turn the eddy currents.

7.0  SEASONS RESULT FROM ROTATION OF THE EARTH ABOUT THE SUN

7.1       The Earth is divided into 6 declinations because its axis of rotation is not perpendicular to the plane in which it rotates about the sun.

7.2       Seasons are produced by the revolution of the Earth about the Sun:

7.2.1   The sub-tropics (between 23.5EN and 23.5ES) generally receive the greatest solar insolation because the surface is inclined towards the sun;

7.2.2   Daylight hours and solar insolation are more variable outside the tropics, so there is greater fluctuation of temperature. 

Acoustics: Human hearing, room acoustics, noise control & sound reinforcement

PAUL HAY Capital Projects

www.phcjam.com

Acoustics

Author:          Paul Hay

e-mail:            paul.hay@phcjam.com

profile:           www.linkedin.com/in/phcjam

1.0   INTRODUCTION TO ACOUSTICS            

1.1_      Sound is an electro-magnetic wave consisting of a series of pressure variations, or vibrations, in an elastic medium.

1.2       Noise is unwanted sound.

1.3       Hertz is the frequency of sound wave cycles per second

1.4       The human voice has a frequency range of 100 to 7,500 Hz.

1.5       Wave-lengths are longer for lower frequencies:

λ = C/f                                                                                                                   1.1

where,

λ =  Wave-length, m

C = Velocity of sound, m/s

f = Frequency of sound, Hz

1.6       The velocity of sound in air is 344 m/s.

1.7       Sound originates at a source and takes a path to a receiver.

1.8       The Inverse-Square Law states that the intensity of an electromagnetic wave is inversely proportional to the square of the distance of path from the source.

2.0   HUMAN HEARING

2.1       Sound audible to humans is within the frequency range 20 - 20,000 Hz.

2.2       Audible frequencies have wavelengths from 17 - 15,200 mm long.

2.3       The threshold of hearing occurs at a sound level of 10^-20 W/m².

2.4       Decibel is the intensity level (IL) equivalent to 10 times the logarithm of a measured sound level (I) over the threshold of hearing (I_o):

IL = 10log(I/I_o)                                                                                                      2.1

2.5       The human ear is less responsive to frequencies at the extremes of the audible range at low sound levels, but this improves as the volume is increased:

2.6       The apparent loudness of sound is also exponential:

2.6.1   A-weighed decibels [db(A)] only measures audible sound with the frequency responsiveness of the human ear at the respective sound level;

2.6.2   0 db(A) is the threshold of hearing;

2.6.3   10 db(A) is an apparent loudness twice that of the threshold of hearing;

2.6.4   60 db(A) is loudness of the human voice; and

2.6.5   130 db(A) is the threshold of pain.          

3.0   ROOM ACOUSTICS

3.1       The acoustics within a room depends on interior noise control; reverberation and room shape.

3.2       Reverberation is the repetition of sound at reduced levels of loudness after sound has ceased from the source.

3.3       Reverberation time (T_r) is the time taken for the sound to reduce to -60db:

            T_r = 0.16 V/3A                                                                                                      3.1

where,

            T_r = Reverberation time, sec.

A = Total absorption at the respective frequency, m²

3A = α_avg x S

α_avg = S₁ α₁ + S₂ α ₂ + ............. + S_nα_n

S₁ +S₂ + .........................S_n

S = Total Surface Area, m²

α_n = Coefficient of absorption at the n^th surface

3.4       The units of total absorption are also called Sabins, in honour of W. C. Sabine, a pioneer in architectural acoustics.

3.5       The coefficient of absorption (α) is the ratio of intensity levels of an absorbed sound and an incident sound:

α  = I_a/I_i                                                                                                                   3.2

where,

I_{a =} Absorbed wave intensity, W/m²

I_{i =} Incident wave intensity, W/m²

3.6       Rooms with Alive@ sound have highly reflective surfaces [i.e. α_avg < 0.2].

3.7       Rooms with highly absorptive surfaces are Adead@ [i.e. α_avg > 0.4].

3.8       Auditoriums and Quiet Rooms require treatment of absorptive material be placed on all surfaces, but other spaces generally require only ceiling treatment.

3.9       The optimum reverberation time for speech can be determined by the relationship:

            T_r = 0.30 logV/10 = 0.35 sec.                                                                             3.3

3.10    Typical volumes for drama and speech are 2.3 - 4.2 m³/seat.

3.11    Concert Halls adjudged excellent for music have reverberation times of 1.6<T_r<1.8.

3.12    Typical volumes for concerts are 6.2 - 11.0 m³/seat.

3.13    Recommended proportions for Music Rooms are 3:4:5.

3.14    Undesirable qualities can result from poor room design:

3.14.1 An echo is a sound reflected at sufficient volume to be heard with a delay greater than 50 ms;

3.14.2 Flutter is a buzzing or clicking sound comprised of repeated echoes between non-absorbing parallel surfaces;

3.14.3 Standing Waves are like flutter but accentuate specific frequencies that have wave-lengths twice as long as the distance between the parallel surfaces.

3.14.4 Standing Waves are only important in rooms that are small relative to the wave-length of the frequency [i.e. <9.1 m for music, and <4.6 m for speech.

3.14.5 Focusing is primarily reflection from concave surfaces that converge at one area, so round buildings should be avoided.

3.14.6 Creep is the reflection of sound along a concave surface from a source at one end to a receiver at the other.

4.0    NOISE CONTROL

4.1       Noise control is exercised by (a) reflecting and absorbing sound within a room, (b) intrusion and attenuation of sound from sources outside the room, and (c) reducing equipment and airflow noises.

4.2       Sound waves are reflected by objects larger than their wave-length.

4.3       Noise Reduction Coefficient (NRC) is an area-weighed average of sound absorption coefficients at frequencies 250, 500, 1000, and 2000 Hz.

4.4       NRC is increased by greater material thickness, composition, and resilience of the installation.

4.5       Effective reduction of outside noise involves keeping sound from going around, under and through a room=s walls, roof and floor.

4.6       Sound waves go around objects smaller than their wave-length.

4.7       Sound Transmission Coefficient (STC) is the measure of sound absorbed in transmission through a building element:

4.7.1   STC measurements are restricted to airborne sound at frequencies of 125 - 4,000 Hz and is therefore relevant to evaluation of speech privacy;

4.7.2   STC does not measure impact noise, low frequency noise (eg. traffic & VAC sources) or amplified music.

4.8       Impact (Structural borne) Isolation Class (IIC) should be equal or greater than STC ratings.

4.9       An architect analyzes and solves a noise control problem in a four stage process:

4.9.1   Establish Permissible Noise Criteria (PNC) for background noise in the respective occupancy;

4.9.2   Identify and measure intensity level of noise;

  

4.9.3   Calculate the Noise Reduction (NR):

NR = IL of noise source - PNC                                                                                    4.1

4.9.4   Specify building element with transmission loss (TL) curves that exceed the required NR curve.

4.10    NR requirements can be reduced by using heavier construction and locating noisy space next to rooms having high PNC.

4.11    Machinery (eg. compressors) which vibrates due to rapidly moving parts should be isolated from the building=s structure.

4.12    Rapid air movement in ducts are also sources of noise:

4.12.1 Noise is reduced by creating smooth transitions from one duct to the next; and

4.12.2 Noise is reduced by increasing the cross-sectional area of the duct and reducing the air-velocity.

5.0   SOUND REINFORCEMENT

5.1       Sound Reinforcement Systems augment sound that would otherwise be inadequate:

5.1.1   Systems are required in spaces having volumes greater than 1,400 m³; but

5.1.2   These systems cannot achieve complete correction of poor room acoustics.

5.2       Sound Systems comprise (a) input from sources like microphones, (b) amplifiers and controls (such as equalizers), and (c) output from loudspeakers.

5.3       Loudspeakers should give the impression that the sound is originating from the source:

5.3.1   Time delay is necessary because electrical input travels at the speed of light while sound is slower;

5.3.2   Equalization may need to be applied to create a frequency response comparable to the original sound.

5.4       Distributed loudspeaker systems comprise a number of low-level loudspeakers located overhead which may be used as public address systems, where directional realism is not essential.

5.5       The sound system operator must be able to hear the sound as the audience.

 

FURTHER READING

            Mechanical and Electrical Equipment for Buildings, 8^th edition, Benjamin Stein, John S. Reynolds, John Wiley & Sons Inc., USA, 1992

            Ramsey/Sleeper Architectural Graphic Standards, AIA, Robert T. Packard (ed), John Wiley & Sons Inc., USA, 1981

Solid Waste Disposal: planning requirements & equipment

PAUL HAY Capital Projects

www.phcjam.com

  

Solid Waste Disposal

Author:          Paul Hay

e-mail:             paul.hay@phcjam.com

profile:            www.linkedin.com/in/phcjam

1.0         SOLID WASTE DISPOSAL USES ENERGY AND SPACE

1.1            Energy is first used to package and transport goods then to collect them as trash.

1.2       Trash compactors also have energy and space requirements.

1.3       Provision for the delivery of supplies, collection and storage of solid waste can (a) require more space than other disposal systems; (b) present a fire hazard; and (c) can create serious local environmental problems.

1.4       Solid Waste is considered as either Ahigh grade@ or Alow grade@ resources: the former being recyclable and the latter fuel for incineration.

1.4.1    High grade resources include aluminum, steel, paper, cardboard and some plastics;

1.4.2    Incineration of low grade resources may cause air pollution and ash-disposal problems.

1.4.3    Low grade resources should be kept clean and dry before burning.

1.5       The earlier resources are separated the less energy will be used.

1.6       Recycling saves energy.

1.6.1    50% less energy is used to produce cardboard from recycled material;

1.6.2    52% less to recycle steel; and

1.6.3    96% less to recycle aluminum.

1.7       Anaerobic combustion in enclosed land-fills will generate methane gas after many years, and this can be used to support generation of electricity and co-generation: where heat is recovered from the generating process.

2.0         DISPOSAL OF RESIDENTIAL WASTE SHOULD BE PLANNED

2.1       Solid waste should be stored in well ventilated spaces.

2.2       The Kitchen is generally the location for storage of solid waste in residences.

2.3       A better location for storage of residential waste is in a room entered from the Kitchen and opening to the outdoors.

2.4       Garbage disposal units grind organic food scraps and dispose of them into the central sewer where they are better able to bio-degrade than in landfills.

2.4.1    Water and energy are used in the process.

2.4.2    The central sewers also require more energy to treat the increased flow.

2.4.3    Moisture is reduced in garbage receptacles which keeps waste in a better condition for incineration; and

2.4.4    Weight of garbage is reduced in the process.

2.5       Garbage compactors are not necessarily advantageous.

3.0       DISPOSAL OF WASTE NEEDS TO BE FACILITATED IN LARGE BUILDINGS

3.1       Industrial and commercial processes generate waste of all types: some being toxic.

3.2       Collection of waste is a three stage process.

3.2.1    Waste generated at work stations are initially placed in bins provided.

3.2.2    Bins are emptied into collection carts which are stored in service closets until full;

3.2.3    These closets have service sinks to wash the bins; and

3.2.4    In the final stage, trash is transported to the ground floor via service elevator for further storage and processing.

3.3       Storage spaces need to be cool, dry and well ventilated.

3.3.1    Burnable trash can be shredded and incinerated.

3.3.2    A sprinkler system is advisable; but

3.3.3    Regulations may limit use of incinerators.

3.4       The garbage is finally collected and transported away from the building.

Fig. 1: Stages for Collection of Waste [Source:- Mechanical & Electrical Equipment for Buildings]

4.0         SPECIALIZED EQUIPMENT MAY BE USED

4.1       Incineration reduces waste transported to landfill.

4.2       Modern incinerators produce less pollution and facilitates heat recovery.

4.2.1    Hot water or steam is produced.

4.2.2    In large-scale operations, steam produced can be used to generate electricity.  
  

4.3       Garbage can be compacted and bagged.

4.4       Compactors can reduce the volume of trash by 90%.

4.4.1    Compactors need to be vibration-isolated.

4.4.2    Some compactors are manually free standing and others automatic chute-fed.

4.4.3    Many have built-in sprays for fire control and disinfection.

4.4.4    Access to water and floor drains is desirable.

4.5       Pulping systems (a) reduce air pollution that may result from use of incinerators, and (b) reduce space needed for storage.

4.5.1    Water is introduced and waste ground into pulp.

4.5.2    90% of water is extracted by a water press to leave a transportable slurry.

4.5.3    The volume of waste is reduced by 20%.

4.5.4    Extracted water is re-used.

4.5.5    Pulping systems should not be used for metals or plastics.

4.6       Vacuum systems use a grinder and evacuation tube.

4.6.1    Air is used as the medium for transportation.

4.6.2    Lines are small and waste can be moved horizontally or upwards.

Fig. 2:  Pulping System [Source:- Mechanical & Electrical Equipment for Buildings]

FURTHER READING

            Mechanical and Electrical Equipment for Buildings, 8^th edition, Benjamin Stein, John S. Reynolds, John Wiley & Sons Inc., USA, 1992

Conveyance Systems: escalators, elevators, etc.

PAUL HAY Capital Projects

www.phcjam.com

Conveyance Systems

Author:          Paul Hay

e-mail:            paul.hay@phcjam.com

profile:           www.linkedin.com/in/phcjam

1.0   MECHANICAL DEVICES MOVE PEOPLE & FREIGHT

1.1_      Moving Walks and ramps are used to (a) assist in walking long distances, (b) transport large and bulky objects, and (c) reduce congestion:

1.1.1   Inclines up to 15E can be provided;

1.1.2   Maximum allowable speeds depend on the inclination and design approaches.

1.2       Pneumatic tubes transport cylinders containing paperwork, money, etc. from one end of a tube to another:

1.2.1   Sizes range from 50 mm diameter to 150 mm x 450 mm (for x-rays);

1.2.2   Air pressure propels the cylinders through the tubes; and

1.2.3   Complex systems use computers to deliver cylinders to pre-selected locations along the tube.

1.3       Endless belt conveyors carry paperwork horizontally in packs or vertically in slots.

Figure 1: Conveyor System

[Source:- AIA Architectural Graphics Standards]

1.4       Trays and dumbwaiters carry paperwork, food, etc. between departments in large commercial buildings or between floors of multi-storey buildings:

            1.4.1   Tray systems automatically transport trays via moving carriers between dispatch cut-outs at intervals along a chain;

1.4.2   Dumbwaiters use ropes and pulleys to transport items on cars or platforms through a vertical shaft:

1.4.2.1            They can be manual or automatic;

1.4.2.2            Manual operation is limited to two floors;

1.4.2.3            They are used in restaurants, libraries, and offices;

1.4.2.4            Vertical shafts should be installed adjacent to other vertical shafts.

1.5       An escalator is a mechanical staircase with moving treads which transport standing pedestrians.

1.6       Elevators can be electric traction or hydraulic.

2.0   ESCALATORS ARE MORE EFFICIENT THAN ELEVATORS

Fig. 2: Escalator

[Source:- Mechanical & Electrical Equipment for Buildings]

2.1       Escalators occupy a fifth of the space elevators require to transport comparable amounts of people.

2.2       A sixth less escalators are required to move comparable amounts of people.

2.3       Escalators are typically 800 mm or 1,000 mm wide between handrails.

Figure 3: Escalator in crisscross arrangement

[Source:- Mechanical & Electrical Equipment in Buildings]

2.4       They are usually installed in pairs:

2.4.1   They can be installed in parallel or criss-cross;

2.4.2   Treads and handrails are inclined at 30E from the lower floor;

2.4.3   50 m² space should be provided at either end of the escalator to facilitate easy mounting and dismounting.

Figure 4: Escalator in parallel arrangement

[Source:- Mechanical & Electrical Equipment in Buildings]

2.5       Escalators can serve up to 5 storeys.

2.6       Escalators are constructed as a steel-trussed framework:

2.6.1   Motor-driven sprocket wheels at each end revolve to form two chains which pull a conveyor-belt of treads;

2.6.2   Sprocket wheels and chains also move the handrails;

2.6.3   Automatic roller shutters can be deployed over tops of horizontal wellway openings for fire protection on any floor:

2.6.3.1            Sprinklers can be installed on the soffit of the escalators and on the ceiling immediately surrounding the wellway;

2.6.3.2            Blowers on the roof can force fresh air through floor openings; and

2.6.3.3Extractors can exhaust indoor air above the roof.

3.0         DESIGN FOR ELEVATORS INVOLVE THEIR LOBBIES AND CABS

Figure 5: Elevator Lobbies

[Source:- AIA Architectural Graphics Standards]

3.1       Double-decker cabs require escalators to transport people from the ground floor to the upper floor.

3.2       Sky lobbies require the building to be divided into 2 or 3 zones:

3.2.1   Each zone has independent elevator systems using a common shaft;

3.2.2   Express elevators facilitate movement between lobby zones.

3.3       Clear opening for commercial installations is typically 1,050 mm.

3.4       Clear opening up to 1,500 mm wide are available for service elevators and hospitals.

3.5       Centre-opening doors provide the fastest closing speeds.

3.6       Emergency power is recommended as brakes hold cabs stationery during power outages or brown-outs:

3.6.1   Hydraulic elevators and small traction cabs can be lowered manually; but

3.6.2   Emergency power is critical for large cabs, especially express elevators.

Figure 6: Traction & Hydraulic Elevators

[Source:- AIA Architectural Graphic Standards]

4.0   TRACTION ELEVATORS ARE MORE ECONOMICAL TO OPERATE

4.1       Mechanical components include (a) grooved sheave, (b) electric motor with brakes, (c) auxiliary equipment, (d) elevator shaft, (e) guide rails, (f) cab, (g) hoist wire ropes, (h) counter-weight, and (i) safety springs or buffers.

4.2       The sheave, motor and auxiliary equipment are located in a machine room:

4.2.1   The machine room is typically located over the shaft but the motor can be located in the basement; but

4.2.2   Basement location increases power consumption, loading on overhead supports, and wear on ropes;

4.2.3   The room is approximately twice the size of the shaft;

            4.2.4   1 2 additional storeys is required above the top of the beam supporting the elevator shaft.

4.3       Guide rails, cabs, counter-weight, and spring/buffers are installed in the shaft:

4.3.1   Guide rails are placed on each side of the cab;

4.3.2   The hoist wire is attached to the top of the cab at one end, wraps around the sheave, and is attached to the counter-weight at the other end.

5.0        HYDRAULIC ELEVATORS ARE INSTALLED IN LOW-RISE BUILDINGS

5.1       Buildings are typically no higher than 18 m.

5.2       Mechanical components include (a) reservoir, (b) pump, (c) elevator shaft, (d) guide-rails, (e) cab, (f) plunger, and (g) safety springs or buffers.

5.3       The cab is supported by the plunger within the elevator shaft.

5.4       Oil from a reservoir is pumped into the plunger to raise the cab.

5.5       Oil is released from the plunger to lower the cab.

5.6       Plunger may require a hole below the basement floor to a depth equivalent to the travel of the elevator.

FURTHER READING

Mechanical and Electrical Equipment for Buildings, 8^th edition, Benjamin Stein, John S. Reynolds, John Wiley & Sons Inc., USA, 1992

Construction Materials & Processes, Don G. Watson, McGrawHill Book Co., USA, 1978;

Architectural Handbook, Alfred M. Kemper, John Wiley & Sons Inc., USA, 1979