Unit 11 Building Environmental Systems And Control Flashcards
Heating equipment is comprised of all parts of a heating system, except
The boiler and its fittings
Heating equipment parts
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Radiators, convectors, unit heaters, fin coils, steam traps, air vents, pumps
Radiators
Heat transfer may be;
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Radiant, conductive, convective
Radiation
Transmission of energy via electromagnetic waves.
Conduction
Transfer of heat energy from molecule to molecule within an individual substance, or from the molecules of one body to another body
Convection
The movement of matter, and the heat contained within that matter. Only takes place in liquids or gases
Two types of convection
Natural convection or forced convection
Natural convection
Occurs due to fluid density differences, resulting from temperature differences
Forced convection
Involves the use of pumps or fans
In radiators, convection currents eliminate the need for
Fans
Radiators are classified as;
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Floor Type, window type, wall-hung
Older radiators were made of cast iron sections. Modern radiators are made of;
Light steel pressings welded together.
Convection radiator (convector)
Heat transfer is mostly convection. Steam or hot water flows through a copper or steel tube with metal fins attached.
Radiators and convectors should be placed
Against outside walls, especially under windows.
Unit heater
Convector heater which uses a blower or fan to force air through the heating coils, instead of using natural circulation. Results in large heat output
Unit heater configurations
Cabinet units, floor mounted units, surface or recessed wall mounted, ceiling suspended
Unit ventilators or univents
Cabinet type unit heaters. Have heating coils and a blower or fan, as well as an air filter, Dampers and outside air Inlet for fresh air ventilation
Auxiliary equipment in a steam heating system
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Air vents, radiator valves, radiator traps, condensate receiver and pump, vacuum pump
Radiator valves
Special Globe valves, used to control the flow of steam to radiators.
Radiator traps
Allows condensed steam or water to be discharged from the radiator, but prevents Steam from discharging.
As the steam in the radiator gives up its heat to the room,
It condenses to water
Vacuum pumps
Used in large buildings, to draw the condensate away from the Heat exchangers through the condensate piping. Maintains of vacuum, allows condensate to flow more easily to condensate tank and returns condensate back to the boiler
Two most common steam heating system configurations
Two pipe condensate pump system, two pipe vacuum return system
Two pipe condensate pump system
Condensate flows by gravity to a condensate tank, condensate pump Returns the water from the tank through a Hartford Loop, into the boiler
Two pipe condensate pump system, must be ________ in order to return condensate to the boiler at the same rate as the steam is produced.
Balanced
Two pipe vacuum return system
Used in larger buildings, When Gravity flow is difficult to achieve due to the resistance in long runs of return piping
When filling a steam heating boiler, fill the boiler so the level is;
Above the low water cutoff, but low enough to allow the water to expand
Main sources of trouble for radiators and convectors
The valves and The Traps.
Balancing the heating system is a delicate operation, do not _______
Play with balancing valves and cocks
Two pipe direct return system
Uses two mains, supply and return. Each convector is connected to these mains. Return from each convector flows the shortest and most direct route back to the boiler.
Two pipe direct return system is difficult to balance because
Of the different circuit lengths going to each convector, temperature at each convector is the same but flow to the farthest convector is sluggish. This system is seldom used
Two pipe reverse return system
Return from each convector takes the long way to return to the boiler. All circuits are the same length. All convectors receive same flow and is self balancing.
Multi-zone hot water heating system
Several circuits, each one supplies heat to a different Zone in the building. Each zone can be heated to a different temperature, depending on demand.
Multi-zone hot water system, may be used in a building where;
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Basement is used for storage.
First floor is office space, only used during the day.
Second floor is used 24 hours a day 7 days a week.
Advantages of hot water heating compared to steam Heating
Hot water boiler is smaller and more compact.
Piping pitch or slope is not as critical, where proper drainage of condensate is very important for Steam.
Less maintenance costs
Water treatment is simpler and less costly
Disadvantages of hot water heating compared to steam Heating
Considerable power is needed to circulate water.
Greater danger of freezing.
If a leak occurs, more damage will result.
Must be piped to prevent air pockets.
Radiant panel Heating
Heat rooms with sections of ceilings, walls, or floor panels. Most of the heat is by radiation, small amount by convection.
The first time a hot water system is filled, care must be taken to
Vent all the air out of the system. Usually done at high points where the air tends to collect.
Automatic vent valves
Use hygroscopic discs, as long as water is in contact with the disks, they will swell or expand, and seal off vent opening.
Hygroscopic
Readily absorb water
________ Is installed in the first horizontal stretch of the supply piping, after the water leaves the boiler
Air separator or air scoop
Dip tube air separator
Prevents air that collects at the top of the boiler from leaving with the water. Instead, it passes up to the expansion tank
Hydraulic imbalance
Zone circuits do not always have the same flow resistance, due to difference in piping length and number of connected Heating units. As a result, flow of hot water through each Zone may not be the correct amount needed to satisfy the requirements
To correct hydraulic imbalance
Balancing valve is installed in each Zone circuit. Regulates the flow so each circuit receives the proper amount of water. Flow imbalance on same circuit can be corrected with small plug valves, or Cocks, on the outlet of each convector
Riser stop valves
Gate or ball valve should be installed at the start of each Supply Riser, and at end of each return riser. Allows each section to be isolated
Auto fill valve
Pressure reducing valve, keeps the system filled with water and maintains a minimum set pressure.
Circulating pumps are normally installed on
The boiler piping, Downstream of the expansion tank
Water is incompressible, which means
It creates more water pressure as it expands
The modern hot water system has a ______ expansion tank
Closed.
The cushion of air is trapped in the tank, and is compressed when water enters the tank. Results in an increase in the system air and water pressure. Allows for higher operating temperature without running the risk of reaching boiling point of water
With a larger volume of air in a closed expansion tank, there will be
Less variation in the system pressure as the water temperature changes
Bladder type expansion tank
Has a flexible diaphragm that separates the system water from the air. Ensures a permanent air cushion, avoids trouble caused by air escaping into the system
Backflow device
Required to protect building occupants from contaminated boiler water. Installed on the potable cold water feed line to the boiler
Steam to hot water converter
Usually a shell and Tube heat exchanger in which the water to be heated flows through the tubes, and the steam is admitted to the shell surrounding the tubes.
Situations where a steam hot water converter system may be used
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Multi-story buildings, where there would be excessive head on a hot water boiler
When steam is required for kitchen, laundry, sterilizers, or air conditioning
Steam from the boiler is fed to the converter, it is regulated by _____
By a control valve which senses the temperature of the hot water leaving the converter. As the steam gives its heat to the water, it condenses.
Point of no pressure change
The pressure at the point where the expansion tank is connected to the system is practically the same as that in a tank
The boiler pressure in a hot water system should not be affected by the operation of the circulating pump to facilitate this,
The point of no pressure change is nearly always located at or near the boiler
To prevent water from flashing into steam, heating steam pressure must be
Kept above the saturation pressure corresponding to the hot water temperature
To prevent water from flashing into steam, heating steam pressure must be
Kept above the saturation pressure corresponding to the hot water temperature
To prevent the pump from cavitating in a hot water system,
A positive pressure should be maintained in the system at all times.
The pressure at the highest point in the hot water system should be at least _____
12 kpa
Always make sure that the pressure is high enough to give the pump the
Required net positive suction head
The clean hot water system should never be
Drained, except for emergency or servicing of equipment
Antifreeze ______ more than water
Expands
With antifreeze a ______ expansion tank is required
Larger
In residences and small commercial buildings, forced warm air heating systems usually Supply
All the heat required
In larger buildings, the primary heat requirement is often supplied by
Steam or hot water heating system. Secondary warm air heating supplies the remainder of heat required. Secondary system also provides fresh, filtered, heated and humidified outside air for ventilation and humidification
Forced air furnaces are classified by;
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Direction of airflow (horizontal, upflow, or downflow)
Height (lowboy or Highboy)
Type of fuel (gas or oil-fired)
Heating capacity in kj/hour
Efficiency (high, low, or mid)
Highboy upflow furnace
Blower located beneath the heat exchanger, and discharges vertically upward. Air enters through the bottom or side, and leaves the top of the Furnace. Saves on floor space, used in residences or small buildings
Downflow Highboy furnace
Has the blower located above the heat exchanger, and discharges downward. Air enters the top, exits from the bottom. Used in buildings without basements that have Supply ducts in the concrete floor slab, or in crawl space. Found in manufactured homes
Lowboy furnace
Used where Headroom is limited. Blower is located beside the heat exchanger. Cool air is drawn from the top, and warm are discharged from the top.
Lowboy furnaces are a little over _____ in height
1.2m, easy installation in basements of residences and commercial buildings.
Horizontal furnace
Has blower located behind the heat exchanger. Air enters one end of the furnace, and warm air leaves the opposite end of the Furnace.
Horizontal furnace height
About 0.6m high. Used four locations with limited Headroom, like attics and crawl spaces below floors. May be suspended from ceilings
Warm air duct furnace
Heat exchanger and burner equipment section of a forced warm air furnace, mounted directly in the supply duct of a makeup air, ventilating, or air conditioning system. Used in shops and warehouses.
Rooftop heating unit
Weatherproof casing. May have a cooling coil and the heating coil. Fresh air drawn from outside and mixes with Supply are in the mixing section. Found in commercial buildings
Fired space heater
Heats air directly, without the use of ducting. Used in underground parking garages or Automotive Repair Garage.
Types of fired space heaters
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Unit heater, high-efficiency furnaces and heaters, solar heating
Unit heater
Heat exchanger and burner equipment are mounted in a cabinet suspended from the ceiling. Large unit heaters use filters.
Annual fuel utilization efficiency (AFUE)
The higher the AFUE number, the higher the efficiency Out of the Furnace. High AFUE= 90% efficiency or higher.
Electronic ignition eliminates the need for
Standing pilot. Prevents the waste of heat during off periods of the Furnace.
The most widely used application of solar thermal heating uses
Cladding on south facing walls that absorb solar energy
Solar-heated air can either be used
Directly, as a supplement to the existing Heating or process air systems.
A pre warmed source of feed air for industrial furnaces.
Advantages of forced warm air heating
Positive air circulation, for uniform temperature distribution.
Smaller Ducts compared to gravity system
Furnace can be located in any part of the building
Forced warm air heating disadvantages
Are ducks are larger, more difficult to enclose then steam or hot water piping.
Can be noisy if not designed properly
Forced warm air heating disadvantages
Are ducks are larger, more difficult to enclose then steam or hot water piping.
Can be noisy if not designed properly
Over lubricated motor bearings
Oil soaked surfaces cause dust to accumulate, which is a fire hazard. May work into the coils and windings, attack insulation, short-circuiting, burn the motor
Sheave
An adjustable pulley
Ways to check pulley alignment
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Laser light, straight edge, thin wire or string placed on upper and lower sides of both pulleys
A squealing sound coming from the blower compartment on Startup is an indication of
The V belt being too Slack
Simple rule for determining proper V belt tension for blowers less than 1kw
Every 16cm of distance between the pulley rims, belt should have 1 cm of vertical movement
Filters should be cleaned at least
4 times per year
Infrared radiant heating is used in areas that are
Difficult or costly, to heat with other types of heating systems.
Infrared heaters send out
Radiant energy in the form of visible and infrared waves. Waves travel in the straight line through the air, without warming it. When the waves strike a solid, opaque object, radiant energy converts into heat
Spot Heating
Usually only covers small area. Used on loading docks, open work sheds, bus shelters. Also used for snow melting
Types of gas-fired infrared heaters
Surface combustion heater, directly fired refractory heater, internally fired or vented heater, low temperature catalytic heater
Surface combustion heater
Porous or drilled ceramic mat, a metal screen, or wire mesh as the admitting surface. Gas and combustion are mixed in the upper chamber. Mixture flows through the mat and burns on the surface. Heats the surface mat to 760°C to 900°C. Not vented
Directly fired refractory heater
Block of refractory, heated by the burner Flame. Equipped with a reflector, and is unvented. 980°C to 1260°C
Internally fired or vented heater
Most of the heat produced in the heat exchanger is transmitted to the emitting surface, which reaches a temperature of 400°C. Reflectors direct the infrared energy radiated by the emitting surface.
Low temperature catalytic heater
Layer of glass wall with a catalyst, like a metallic salt, and covered with a metal screen. Oxidizes the gas, causes the fuel to burn slowly, without Flame. Results in lower temperature then combustion. Common in oil and gas industry. Intrinsically safe. 315 to 455°C
Two methods of using electricity for Comfort Heating
Direct Heating and indirect Heating
Direct Heating
Heating equipment is installed in the areas to be heated.
Types of direct Heating
Baseboard and wall heaters
Other types of direct heaters
Unit heaters, unit ventilators, radiant panel heater, snow melters.
Indirect Heating
Heat supplied by Electric indirect Energy, transferred to a medium that carries the heat to the areas to be heated
Types of indirect Heating
Electric boilers
Central warm air furnaces, in-duct, and makeup heaters
Advantages of electric heating
Produce no toxic gas, equipment requires less floor space, easy individual room temperature control, lower installation cost, silent operation, lower maintenance
Electric heating disadvantages
Electricity costs are higher than fossil fuels, electrician needed to repair system
Unitary air conditioning systems
Self-contained, packaged equipment installed in, or adjacent to, a zone that provides air conditioning for that area only. Use little or no ductwork.
Benefits of unitary air conditioning systems
Easy to install, low initial cost, used in residential and commercial buildings.
Examples of unitary air conditioning systems
Window air conditioner, packaged air conditioner, unit ventilator, rooftop unit
Examples of unitary air conditioning systems
Window air conditioner, packaged air conditioner, unit ventilator, rooftop unit
Window air conditioner
Direct expansion refrigeration system to cool and dehumidify a local area. Has two compartments, for Supply Air and for the condenser.
Window air conditioner, condenser compartment
Exposed to outdoor air. Houses the compressor, air-cooled condensing coil, condenser fan.
Window air conditioner advantages and disadvantages
Low initial cost, Well Suited For local Cooling in residential and Commercial.
Noisy in operation, wide swings in room temperature do to on off Cooling. No Direct Control of dehumidification.
Packaged air conditioner
Can be mounted on the floor, vertically or horizontally, or suspended in False ceilings. Has a supply fan, the efficiency air filter, direct expansion cooling coil. Single zone operation, but can handle more than window air conditioners.
Packaged air conditioners are suited for
Restaurants, Commercial or retail areas, and rooms, like Laboratories. Used for computer equipment.
Packaged air conditioner advantages and disadvantages
Satisfy more environmental requirements, quieter than window air conditioners, but are still noisy.
They are costly. Dehumidification is provided, but not directly controlled
Unit ventilator
Used to provide individual room control in buildings, that have many zones, but limited for space. Provides Heating and Cooling. No humidification is provided.
Rooftop units
Usually mounted on a roof, adjacent to the area served.
Rooftop units are commonly used for single Zone commercial buildings such as;
Department stores, restaurants, shopping centres, warehouses. may not be suited for multi-zone controls
Central air conditioning systems
Air is conditioned in a central mechanical room. Uses boilers, chillers, air handling units. Installed in larger buildings
Central air conditioning system advantages in comparison to unitary systems
System is easier to operate and maintain. Equipment is not located adjacent to occupied areas.
Central air conditioning systems drawbacks
Large amount of building space required, need for distribution ductwork, larger equipment components
Types of central air conditioning systems
Forced air system, single zone constant Air volume system, High Velocity terminal reheat, multi-zone, dual duct
Forced air system
Most common central system. Normally located in the basement. Single zone operation. Well suited for wood frame Construction. Installed in a small room adjacent to the conditioned space.
Single zone constant Air volume system
Provides a constant volume of air. Similar to rooftop unit, instead installed in the mechanical room.
High Velocity terminal reheat system
Uses higher are velocities for distribution throughout the building. Reduces ductwork cost and space requirements. Needs more powerful Supply fans, with larger Motors. Requires a terminal reheat box for each Zone.
Multi-zone system
Constant volume system, discharge of air is modified to provide multi-zone. Supply air flow in the hot deck and cold deck. Dampers are linked, but 90 degrees out of phase, full opening of cold deck results in full closing of hot deck.
Dual duct system
Hot and cold are mixed to very the supply air temperature to each Zone. Used in larger buildings, Provides constant air circulation rate in each Zone. Can handle more zones than the multi-zone system.
Combined systems
Combines a central air system with supplementary for each Zone. Used for multiple zoning and find control of individual rooms.
Constant Air volume system with perimeter Heating
Used for multi-zone buildings, such as schools. Not suited for larger buildings due to low velocity ductwork.
Fan coil units with make-up air system
Used extensively in motels and hotels due to minimum space requirements and low costs, High degree of individual Zone control. Can be a 2 pipe, 3 pipe or 4 pipe system. 4 pipe system has best control of room conditions on a year-round basis, but higher costs.
Heat pump
Refrigeration equipment is used to remove and discharge heat from a space.
Ex; refrigerator
Induction system
High Velocity primary air induces a flow of secondary room air through the coils. Well suited for use in large buildings with multiple zones, like hospitals.
Variable air volume with perimeter Heating (VAV)
System can vary itself, results in a reduction of 20 to 30% and air capacity. Very energy-efficient. Used in all types of buildings, with diversity of cooling loads and multiple zones.
Any areas of the building that are south-facing will have
A higher degree of temperature fluctuation, due to the radiating heat from the Sun
The ________ is the first line of defense when it comes to reducing energy requirements and the environmental impact of the building
Operator
Operational integrity
Includes boiler and pressure vessel inspections, safety valve inspections, certifications
Thermal transmission (W) or rate of heat flow
Quantity of heat flow from all mechanisms, per unit time. Base unit is the watt.
Thermal conductivity
Thermal heat flow by conduction only, through a unit thickness of a single uniform type of material.
Thermal resistivity, is the reciprocal of
Thermal conductivity
Thermal conductance
The thermal heat flow through a unit area of a non-uniform, composite material.
U-Factor
Thermal conductance for each change in degree of temperature
Thermal resistance is the reciprocal of
Thermal conductance
Thermal resistance
The value of a material’s ability to resist heat transfer or flow. The higher the R-value, the greater the insulating value or resistance to heat flow.
Two major types of heat gains
External and internal heat gains
The transmittance to heat flow is known as
The overall coefficient of heat transmission (U-Factor)
Infiltration
The leakage of outdoor air into a building through cracks and openings
Infiltration load
Heat must be removed from the outside air, to cool it to the indoor design temperature
Two methods of estimating the quantity of air entering by infiltration
Crack method of measuring infiltration
Air change method of measuring infiltration
Crack method of measuring infiltration into a building is based on
The average quantities of air known to enter through doors, cracks of various widths, from around windows and doors when wind velocity is constant.
To calculate heat gain by infiltration (crack)
Determine the types of wall openings (windows and doors) that are creating the infiltration through the wall.
Determine the outside and inside design temperatures
Crack method formula
H = C × Q (t1-t0) × L
H = heat required to raise the temperature of air leaking, to the indoor temperature
C = constant relating to the specific heat of air
Q = volume of air entering the structure
T1 = indoor temperature
T0 = outdoor temperature
L = length of crack around the circumference of all openings
Air change method of measuring infiltration
Way to quickly approximate a source of heat loss. Does not consider nature of the opening, how opening a sealed, effective external wind velocity.
The air change method is
Quicker, but less accurate than the crack method.
Solar heat gains
Result of the radiant rays of the Sun. Do heat space directly, but heat the object or Surface on which they fall. The object or Surface will transmit Heat by conduction, radiation and convection to the airspace.
In calculating solar gains
The occupancy load, orientation of the building, and the type of shading all affect solar gain
How to reduce solar Gains
Windows with reflective glass, heat-absorbing glass, awnings, Shades, blinds
Internal heat gains include
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People, lighting, Motors, equipment, food
Cooking equipment installed in a conditioned space without a hood and exhaust fan, is estimated as a heat gain of
50%
Infiltration can be reduced by
Thoroughly caulking around frames, and by weather stripping doors and windows
ASHRAE guidelines for minimum air ventilation in residential buildings
3.5L/s per person or 0.15L/s per m2 of floor space, for normal occupancy of one person per 25m2
Infiltration is not an effective way to
Provide necessary ventilation
The arbitrary reduction of ventilation rates to save energy is
Poor practice. Losses in employee efficiency and increased sick time may more than offset the savings.
Once through air conditioning system
Air is not recirculated, either in the rooms, or in the system
Methods of heat recovery from air conditioning systems
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Runaround around system, thermal wheel, heat pipe
Runaround system
Two fin tube heat exchangers, heat moves from one coil to another. Recovery coil is installed in the ductwork handling exhaust air. The preconditioning coil, installed in the ductwork that introduces makeup air.
The recovery coil extracts
Warm exhaust air, before it is discharged to the outdoors. Heat is absorbed by the circulating liquid, and carried to the preconditioning coil, where it’s transferred to the cold ventilation air.
When freezing is possible _______ is used
Ethylene glycol
Runaround system heat recovery range
45% to 55%
Several names for the thermal wheel
Rotary regenerative heat exchanger, heat wheel, energy transfer wheel, Ljungstrom wheel
Thermal wheel
Uses a single exchange unit, the mass of the material of the rotor serves as the heat carrier.
Hygroscopic recovery wheel
Used when transfer of both sensible and latent heat is desired
Thermal wheel disadvantage
Requires expensive ductwork modifications
Thermal wheel
sensible thermal recovery and latent heat thermal recovery
60-70%
20-50%
Heat pipe
Tube with a capillary Wick structure consisting of fine circumferential striations machine on its internal surface.
process to process
Heat is recovered from a process, and fed back into the process
Ex;Paint drying ovens, spray dryers and brick Kilns
Process to comfort
Heat is recovered from a process, and used to heat makeup or ventilation air
Comfort to comfort
Recovering heat of the exhaust Airstream to preheat ventilation air during winter
Heat pipe with preheat coil
Preheat coil in the ventilation Airstream, on the inlet side of the recovery unit.
Conditioned air usually includes
Make-up air, which is also called outside air (OA)
Accepted value of ____ minimum OA
15%
Two of the most important factors in the cost of fan operation
Air quality and cleanliness
Preheat coils
Used to preheat the fresh outside air prior to mixing with return air
Heating coils
Used to heat the mixture of return air (RA) and outside air (OA) prior to Distributing this Supply Air (SA) to the building
When the temperature rise of more than 18°C is required,
Multiple preheat coils are used
The greatest chances for freezing occurs when the air temperature transitions from
1°C to sub-freezing.
The source of heat and the ______ determine the best control strategy to use
Mechanical design
Static pressure is usually in the range of
40 to 50 kPa. When static pressure rises above 50 kPa, air velocity in the duct May generate too much noise and cause excessive air flow. When it drops below 40 kPa, system may have operational troubles.
In order to maintain a positive building pressure,
The static pressure is measured in the Supply Air Duct, and the volume of air that is supplied to the building is manipulated to maintain the building pressure
When the duct static pressure drops below set point,
The fan speed increases and outside air damper opens further.
When duct static pressure rises above set point,
Fan speed decreases and outside air damper closes further.
Are imbalances are evident when
People struggle to open or closed doors due to excessive air pressure differential
