HVAC and Lighting Systems in Buildings Notes

HVAC SYSTEMS IN BUILDINGS

Factors Affecting Human Thermal Comfort

• We can manipulate factors to achieve thermal comfort through design.

Thermal Nature of Human Body

• Human body is an object that:

  • Generates energy from food.

    • $Glucose + oxygen \rightarrow carbon dioxide + water + energy$

  • Exchanges sensible heat with its environment through radiation, convection, and conduction.

  • Loses latent heat by evaporation.

  • Is capable of adapting to conditions to regulate temperature.

Human Thermal Comfort

• Definition: Environmental conditions within which the human body can adapt easily.

• The body always tries to keep its core temperature between 36°C and 38°C by adjusting blood circulation.

Variables Affecting Human Comfort

• Four environmental factors:

  • Air temperature (e.g., -5°C vs. 23°C vs. 45°C).

  • Relative humidity (e.g., 10% vs. 50% vs. 90%).

  • Air speed (e.g., in front of a fan ≈ 2m/s).

  • Mean Radiant Temperature (temperature of the surrounding surfaces, e.g., hot windshield in the sun).

• Two human factors:

  • Activity (e.g., sleeping vs. playing football).

  • Clothes (e.g., swimming suit vs. business suit vs. snow coat).

Bioclimatic Chart

• Used in determining strategies of achieving thermal comfort.

Machines for Human Thermal Comfort

• Categories of active HVAC systems.

• Environmental issue for Architecture Thermal Issues.

Categorization of HVAC Systems

• Heating systems vs. cooling systems.

• Local systems vs. central systems.

• Air systems vs. water systems.

Fundamentals of Mechanical Cooling/Heating Systems

How to Acquire Heat

• Heat is easy to get through many means:

  • Burn a fire using any combustible materials (e.g., Wood, Gas, Diesel, etc.).

  • Capture solar energy.

  • Capture underground high temperature of the earth (geothermal).

How to Acquire Cooling

• Cooling is much more difficult to acquire than heat.

• Most common methods:

  • Mechanical refrigeration.

  • Absorption refrigeration.

• In addition to evaporative cooling.

Principles of Mechanical Refrigeration

• When a gas is mechanically liquefied using a compressor, it releases its latent heat (in the condenser).

• When the pressure on the liquid is lowered, it evaporates back into a gas (in the evaporator) and absorbs the needed latent heat from the surrounding. The surrounding then becomes cold.

• Components: Compressor, Condenser, Evaporator, Valve.

Evaporator and Condenser

• Evaporators cause chilling (cooling), hence the name “Chiller.”

• Condenser produces heat and has to be cooled down.

  • Two ways to cool down the condenser:

    • Using Air (machine needs to be put in a well ventilated area).

    • Using Water (a cooling tower is used and needs space).

    • We may also lose the heat to earth or a body of water (e.g., lake).

Cooling Towers

• Needed to reject the heat generated by the chiller.

• Air passes on hot water to cool it down.

• They create a microclimate of high humidity air.

• In cold weather, they create fog.

• Very noisy because of air speed.

Selecting Central or Local System

• It is a major decision that has important implications on architecture.

Comparison of Central and Local HVAC Systems

• Central system:

  • One or several large mechanical spaces.

  • Sizable distribution tree.

  • Complex control system.

  • Breakdown in central equipment can paralyze the entire building.

  • Can be energy consuming with variable zone schedules.

  • Easier to control noise, heat, and air quality.

  • Easier to maintain.

  • Easier to have energy recovery strategy.

• Local systems:

  • The opposite in terms of advantages and disadvantages.

Types of Local Systems

• Fans.

• Unit air conditioner.

• Evaporative coolers.

• Small room heaters.

Local Cooling Systems - Fans

• Improve comfort by increasing air speed.

• Generally, people will perceive 1°C decrease in air temperature for every 1 m/s increase in air speed.

• People may be dissatisfied if air temp is low and wind speed is high.

Local Cooling Systems - Unit Air Conditioner

• Most commonly used in small buildings.

• Can be:

  • Window unit

    • Very noisy.

    • Air supply has to come from external wall side.

  • Split system

    • Less noisy.

    • Air supply can be located anywhere in the room.

Local Cooling Systems - Evaporative Coolers

• Used in hot and dry weather.

• Air is cooled by evaporating water.

• The relative humidity is increased.

Local Heating Systems - Small Room Heaters

• Gas heaters.

• Electric Resistance Heaters.

  • Three techniques to distribute the heat:

    • Natural convection.

    • Radiant heating.

    • Forced air.

Major Components in a Central HVAC System

• Distribution:

  • Pipes, ducts, diffusers, grilles, fans, pumps, radiators.

• Control system:

  • Thermostat, valves, dampers.

• Heating and cooling equipment:

  • Chillers, boilers, furnaces, heat pumps, cooling towers.

Possible Distribution Concepts

• Vertical and horizontal ducts

Major Components in a Central HVAC System - Distribution

• Possible distribution concepts (AHU and horizontal ducts).

Major Components in a Central HVAC System - Distribution

• Integration of distribution elements with the suspended ceiling.

Major Components in a Central HVAC System - Control

• Air Dampers

  • Opens and closes (automatic or manually) to control the volume of air that passes to the space.

• Thermostat

  • Controls the desired temperature in a space (or a zone).

Difference Between Water and Air Distribution Systems

• In a central system, we typically distribute the cooling (or heating) using one or both of the following two systems:

  • Air distribution systems

    • Use air to carry the cooling (or heating) from the central equipment to the space directly.

    • Distributed air is then mixed with space air to achieve required air temperature.

  • Water distribution systems

    • Use water to carry the cooling (or heating) from the central equipment to a “water-air exchange unit” then to the space.

    • Distributed air is then mixed with space air to achieve required air temperature.

    • In the case of hot water heating systems, water is distributed directly to the spaces. The space is heated by radiation and convection method (no air mixing).

Water Distribution Systems - Radiant Panel Heating / Cooling

• Utilizes heated/cooled floors as radiant surfaces.

• The heating/cooling is carried by water to the space and distributed as hidden pipes in the floor.

Integrating Mechanical and Interior

• Such integration can happen at several levels:

  • Touching

    • One system rests on top of another and held in place by gravity.

  • Connected

    • Physically connected by clips, nails, bolts, …

  • Meshed

    • Occupy the same space.

  • Unified

    • Shares the physical form and no longer distinct from one another.

• Note: This discussion on integration is based on the Building Systems Integration Theory presented in the book: Rush, R., “The Building Systems Integration Handbook”, The American Institute of Architects

Mechanical and Interior (touching)

• The interior component rests on the mechanical component.

  • (e.g., carpet on electric wire).

• Typically, this integration occurs on floors.

Mechanical and Interior (connected)

• The two systems are connected with bolts, screws, ties,..

• Functions and materials are separate in every system.

• Usually, both systems are connected to the structural system for support.

• Usually, this relation is combined with meshed or unified relation.

Mechanical and Interior (meshed)

• The mechanical system shares the same space with the interior system.

• Functions and materials are separate in every system.

• Dimensional coordination and material compatibility are issues of concern.

Mechanical and Interior (Unified)

• Both systems share function, material, and space.

• The mechanical component is expressed as interior component.

Accommodating HVAC components

• Determine the type, location, and distribution elements for a central HVAC in a shown villa.

• In particular, you need to define the following:

  • Air system vs. Water system. Hence, the type of needed equipment.

  • Location of FCU (if needed).

  • Location of the pipes/ducts (as needed).

  • Location of supply and return grills.

• Make sure to make appropriate decisions so you do not have ducts or other components interrupting the architecture design of the spaces (unless on purpose).

LIGHTING SYSTEMS IN BUILDINGS

What is Light?

• Can be defined as visually evaluated radiant energy.

• Visible light has a wavelength range from:

  • $380 \times 10^{-9}$ m (Violet) to

  • $770 \times 10^{-9}$ m (red)

• White light is the simultaneous presence of all visible wavelengths in equal (energy) amounts.

Transmittance of Light

• Coefficient of transmission ($\tau$):

  • Is the ratio of the total transmitted light to the total incident light.

    • e.g.: Clear glass 80%

• Types of transmittance:

  • Non-diffused.

  • Diffused.

• When light passes through non-opaque material, some of it does not transmit.

Reflectance of Light

• When light is incident on a surface, some of it may reflect back.

• Coefficient of reflectance ($\rho$):

  • The ratio between the total reflected light and the total incident light.

    • A mirror is almost a perfect reflector.

    • A matte finish black paint is almost a complete non-reflector.

Types of Reflectance

• Specular.

• Diffuse.

• Combined.

Light Units and Terminology

• Luminous Intensity (I)

  • Measures the perceived power emitted by a light source in a particular direction per unit solid angle

  • Units: Candela (CD) – basic unit of light

    • This is similar to saying: Meter is the basic unit for length.

  • An ordinary wax candle has a luminous intensity approximately one candela.

Light Units and Terminology

• Luminous flux ($\phi$)

  • Measure of flow like flow in hydraulic systems (gpm) and current in electric system.

  • It is the rate of flow of luminous energy.

  • Unit: Lumen (lm)

    • Assuming one candela source radiating light equally in all directions and surrounded by a fully transparent sphere that is 1 m in radius, then one lumen will be emanating from 1 m2 of the sphere surface.

  • 1 candela source produces $4\pi(1)^2 = 12.57$ lumen.

Light Units and Terminology

• Illuminance (E)

  • The quantity of light incident on a surface.

  • Units: Lux (lx)

    • One lux is the illumination on a surface uniformly receiving 1 lumen per 1 m2

  • Illuminance = Luminous flux / area = lm / m2

  • The American standard unit for illuminance is foot candle (fc) = 10.764 lux.

Light Units and Terminology

• Luminance (L)

  • Is the luminous intensity of a surface emitting or reflecting light in a certain direction

  • Units: candela / m2 (cd/m2)

• Brightness

  • Is the psychological sensation of luminance.

  • Depends on receiver not the source.

Inverse Square Law

• As the same amount of lumens coming from a source falls on a larger area when the distance is longer then:

  • Lux1 = lumen / area1 and

  • Lux2 = lumen / area2

  • Manipulating the two equations:

    • Lumen = lux1 / lux2 = area2 / area1 = 4D2² / 4D1²

• The further you go from the source (the value of D), the less the illumination in square ratio.

Candle Power Distribution Curves

• Different light sources produce light in different ways.

• These curves show light output produced by:

  • Bare lamp

  • Luminaire

Correlated Color Temperature (CCT)

• The color temperature of a light source is the temperature of an ideal black-body radiator (in °K) that radiates light of a color comparable to that of the light source.

• Warmer colors have lower black-body temperature and cooler colors have higher black-body temperature.

• It basically tells you the color of the light itself.

Lamp CCT

• Each lamp produces light in a certain range of color.

• To select a lamp with an appropriate color or to match lamps that work together, you need to know the CCT of the lamp.

Color Rendering Index (CRI)

• Measures the ability of a light source to reveal the colors of various objects faithfully in comparison with an ideal or natural light source.

• Light sources with a high CRI are desirable in color-critical applications such as art restoration.

Luminous Efficacy (lumen / Watt)

• Is a measure of how well a light source produces visible light.

• It is the ratio of luminous flux to power.

• The higher the value, the better an electric light source is.

Artificial Light Sources

• Incandescent lamps

• Fluorescent lamps

• High intensity discharge lamps

• LED lamps

Incandescent Lamp

• Produces light by heating a high resistance filament to incandescence

• Filament can be straight, coiled, or coiled coil.

• Has many bulb and base shapes

Incandescent Lamp - Advantages

• Low prices.

• Instant start and restart.

• Simple installation with no accessories.

Incandescent Lamp - Disadvantages

• Low efficacy (≈15 lm/w)

• Short lamp life.

Fluorescent Lamps

• Produce light by emitting electrons from cathodes at their end.

• The electrons activate the fluorescent coating on the inside of the bulb.

• Can have many shapes and colors.

Fluorescent Lamps - Advantages

• Long life (average 12000 hours)

• Low cost

• High efficacy (≈70 lm/w)

• Wide range of colors

Fluorescent Lamps - Disadvantage

• Traditionally large size which creates storage, handling, and relamping difficulties.

• May require extra accessories (starter)

High Intensity Discharge Lamp

• Produce light by passing an arc through high pressured special gases

  • Mercury-vapor lamp

  • Metal halide lamp

  • Sodium-vapor lamp

  • Xenon lamp

High Intensity Discharge Lamp - Advantages

• Long life (over 20000 hours)

• High efficacy (≈90 lm/w)

High Intensity Discharge Lamp - Disadvantage

• Produce uncomfortable heat

• Expensive

• May take a long time to work

Light Emitting Diodes (LED)

• Works by passing electricity through a semi conducting material.

• A plastic cover directs the light.

Light Emitting Diodes (LED) - Advantages

• No filament to burn.

• High Efficacy (≈300 lm/w).

• Very little heat is generated.

Light Emitting Diodes (LED) - Disadvantage

• Relatively expensive.

IP (Ingress Protection) Rating

• Example LED lights with IP67 ratings give complete protection against solid and water

Types of Lamp Base

• Lamp base needs to match its connection in the lighting fixture.

• There are standard base types. Each has a code.

• Examples: From the cover of a lighting fixture that has two lamps (IKEA)