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Mechanical Systems

Terms in this set (50)

What systems do mechanical systems include?
heating + cooling, plumbing, and fire protection
What is a plenum?
The space between the ceiling and the structural floor above used as a passage for ductwork, piping, wiring, and return air space. Building codes limit the use of combustible and hazardous materials in the plenum.
What is VAV? (variable air volume)
VAV or variable air volume (as opposed to constant air volume, CAV)With variable air volume systems, the VAV box varies the quantity of air. One duct leads in and one or more lead out and is attached to registers mounted in the ceiling. A VAV box is placed in the plenum near the space it serves.
Both water-cooled chillers and air-based cooling systems contain the following (4) components?
1. Evaporator
2. Compressor
3. Condenser
4. Expansion Valve

Liquid refrigerant flows over an evaporator tube bundle. As it evaporates, it absorbs heat from the chilled water circulating through the bundle.

The compressor draws refrigerant vapor out of the evaporator, pumps it to the condenser, raising its pressure and temperature. As refrigerant condenses on or in the condenser tubes, heat is emitted, cooling the water or air.

Next, the high-pressure liquid refrigerant passes from the condenser through the expansion valve, reducing the pressure and temperature as it enters the evaporator. It then flows over the chilled coils absorbing more heat and completing the cycle.

The difference between air and water-based systems begins at the condensing stage.
When are all-air systems preferred in projects?
They are preferred for projects with poor quality makeup water or in areas with higher water costs. These systems need access to a lot of fresh air, resulting in more space required to house them. The main disadvantages are the bulky ductwork and the considerable fan power required
What is a Single-duct system with CAV
The single-duct system is a one-zone system. A separate supply duct and the air-handling unit are required for each zone. This system is used for small or medium-sized buildings with few zones.
What does CAV stand for?
Constant Air Volume
What is a VAV system?
This single-duct system can have many zones. But VAV systems cannot heat one zone while cooling another, so they are cooling-only systems. A separate heating system can be used with the VAV system. It has a low initial cost and low energy usage. It can be used for almost every building type.
What is a Terminal reheat system (CAV)?
Instead of VAV boxes, this system has terminal reheat boxes that reheat previously cooled air. The zone with the greatest cooling load determines how much air is cooled for the entire building.All other zones then reheat the cold air to the desired temperature using electric-strip heaters or hot-water coils. Most of the building is heated and cooled simultaneously — a waste of energy.
What is a Terminal reheat system (VAV)?
Terminal reheat systems can also be of the VAV type. In this case, the terminal reheat box also controls the volume of air. Varying the volume of the supply air manages the temperature. The reheat function is used only when some space needs heating while the others all need cooling.
What is a multizone system?
Every zone receives air at the required temperature through a separate duct. A multizone air-handling unit custom-mixes hot and cold air for each zone—thermostats in each zone control motorized dampers in the air-handling unit.

The multizone unit is supplied with hot water, chilled water, and fresh air. Because mixing hot and cold air creates a moderate temperature, this system is less energy efficient. Initial costs are higher because of the duplication of ducts.
What is a Double-duct system?
The double-duct system mixes hot and cold air to achieve the required air temperature. Mixing boxes are located throughout the building instead of a central unit. There is no limit to the number of zones possible. Two sets of large supply ducts are necessary.

Double-duct systems create a high level of thermal comfort and allow for zoning flexibility. They are very expensive, not energy-efficient, and require more building space.
What (4) things does a water cooling system require?
1. cooling towers
2. condenser water pumps
3. reservoirs of cooling fluid
4. make-up water pumps
which is more expensive, air-based coolers or water-based coolers?
water-cooled chiller

Initial costs for a water-cooled chiller are also higher. But these systems often last longer than air-based coolers. They have a lower life-cycle cost to offer a better return on investment.

They are most appropriate when a large amount of ventilation is unnecessary or windows can be opened
What is a fan-coil system?
The fan coil unit consists of a fan and a coil in which water circulates. These units are often in cabinets placed under windows. The fan blows room air across coils through which either hot or cold water circulates. Thermostatic valves regulate the flow of water through the coils.

With four-pipe systems, heating or cooling is possible at any time of year. In less expensive two-pipe systems, hot water circulates during the winter and cold water in the summer. An occupant cannot choose between the two, so they can be less comfortable.
What is a Water-loop heat-pump system?
With this system, each zone is heated or cooled by a separate water-to-air heat pump. A thermostat in each zone determines whether the heat pump extracts heat from a water loop (heating mode) or injects heat into the water loop (cooling mode). This system is most appropriate where simultaneous heating of some zones and cooling of others is required.
What are Passive chilled beams?
These chilled beams are similar to active chilled beams (see combination systems below) except that no air supply is used. They work purely by natural convection.

Without forced convection to blow air down, passive chilled beams can only cool. It takes more passive than active chilled beams to cool an area because of the slow motion of natural convection.
What is the main purpose of a combination system?
These systems supply both air and water to each zone of a building. This increases the complexity of the mechanical systems but decreases the size of the equipment. Air is supplied for ventilation.
What is an induction system?
Induction units are usually located under windows. They use water for heating or cooling and neutralize heat gain or loss through the building envelope. A small amount of high-velocity air provides ventilation and air movement.

Thermostats regulate temperature by controlling the flow of hot or cold water through coils.
What is a Fan-coil with supplementary air?
This system also consists of two separate parts. For ventilation and cooling of the interior areas, there is an all-air system. Fan coil units around the building perimeter neutralize heat gain or loss.
What are Radiant panels with supplementary air?
Similar to radiant heating but in reverse, this type of system cools the ceiling. It cools large areas and distributes the cooled air throughout the space.

Cooling with a radiant ceiling works best in dry climates. Humidity control prevents ceiling rain from condensation.
What are Active chilled beams?
Unlike a cold radiant ceiling, chilled beams cool by convection. Chilled beams can be recessed in a suspended ceiling or hang free. They can also incorporate lighting, sensors, and sprinklers.

The active chilled beams can be used for heating because of the forced air ventilation. Chilled beams also work best in dry climates. Otherwise, humidity control is required.
What are common conflicts regarding HVAC on the Practicum Exam that the designer must consider?
1. Plenum height and spacing must be adequate for system requirements. The interior designer must consider the size and spacing of ducts, air handlers, mixing boxes, and piping.

2. The designer may need to lower the ceiling to allow for space between mechanical equipment and recessed items, such as lighting. Refer to the building section to see whether lowering the ceiling will drop it below the head and upper window casings.

3. The designer may need to reselect or relocate any recessed items to ensure enough plenum space.

4. Items cannot be relocated where they will interfere with the location of plumbing, including the floor above.
What are common conflicts the designer will have to identify on the Practicum Exam regarding air supply/returns?
1. Recognize the drawing symbols referenced in the mechanical legend, including circular, square, or slot diffusers.

2. Enclosed rooms or areas should have both an air supply and return. You may be required to spot mistakes with this. The placement of grilles, registers, and thermostats can affect the layouts of furniture and systems panels.

3. Window treatments can affect the heating and air conditioning load in the space and should be spaced a minimum of 2″ away from the glass.
What are common conflicts the designer will have to identify on the Practicum Exam regarding thermostats?
1. In reviewing mechanical plans, ensure that the thermostat is not located on or affected by heat from the window.

2. Thermostats should be mounted at approximately 48″ A.F.F. (1219 mm) within the accessible side and forward reach ranges without obstruction by furniture.
What are common conflicts the designer will have to identify on the Practicum Exam regarding ductwork?
You'll need to know how to read duct sizes on plans. Ducts are labeled as W x H. The first number refers to the width of the duct, while the second represents its height. So, 16 x 14 means a sixteen-inch by fourteen-inch duct.

1. Trunk lines or main duct lines are larger than the branch lines.

2. Smaller branch lines may be relocated when under the size specified in the program or specific test item.

3. Supply air diffusers can easily be relocated when connected with a flexiduct.
What are common conflicts the designer will have to identify on the Practicum Exam regarding access panels?
The air handler will usually require a minimum 2′ x 2′ (609 mm x 609 mm) or 2′ x 4′ (609 mm x 1219 mm) access panel located either directly below or adjacent to the unit. However, it can not be placed where the ductwork connects to the unit.

1. The access panel cannot be in the same location as lighting, a sprinkler head, or other ceiling mounted items.

2. The "V" on the door symbol points towards the hinge location, which should not interfere with access to other items.
What are the (4) causes of IAC?
1. Contaminants from indoor sources. These can include tobacco smoke, formaldehyde, and VOCs from building materials and finishes.

2. Contaminants from outdoor sources may be introduced when venting or windows are improperly located. For example, windows near parking garages bring in the exhaust.

3. Biological contaminants such as mold, mildew, bacteria, mites, pollen, and animal dander.

4. Poor ventilation or inadequate supply of fresh air. In this case, pollutants are not diluted or flushed out.
What is Sick building syndrome?
If health symptoms can't be traced to a particular source but disappear after the occupant leaves the building.
What is Building related illness?
If health symptoms are linked to a particular building contaminant. In this case, symptoms don't resolve after leaving the building, as with Legionnaires' disease.
What is Multiple chemical sensitivity?
This condition is caused by exposure to chemical contaminants. Long-term sensitivity may recur with each exposure to the chemical.
According to CIDQ, what are the (3) items of HVAC coordination Interior Designs are required of?
Placement, style and finish of mechanical, electrical, plumbing, and fire-protection devices, fixtures, and appurtenances (i.e., accessories) with the design of the interior environment.

Ceiling materials and heights; interior partition locations.

Working closely with contractors to respect budgetary constraints and contribute to value engineering efforts
What is a common example of an all-air system?
A residential forced-hot-air furnace

A boiler powered by oil or gas heats air that is distributed throughout the house in ductwork

If necessary, an air conditioning unit is connected to the same ductwork to provide cooled and dehumidified air
How does an all-water heating system work?
all-water heating systems use some type of coil unit called a convector in each space through which hot water is circulated. The hot water heats the fins of the coil unit, and air is heated as it is drawn over the fins. The air may be circulated by convection, as with most baseboard residential fin-tube radiators, or by forced circulation created with a fan
What are terminal reheat systems?
combination systems that use ductwork for supplying fresh air but use water to heat or cool the air before it is introduced into the conditioned space
What is a chase?
This is an enclosed vertical space used only to accommodate ducts or pipes.

In multistory buildings, a chase runs continuously through the floors
What is a mixing box?
A mixing box adjusts the quantity to temperature of air going into a space from the main air supply line(s), reduces the velocity of air, and attenuates noise.

Lines from thermostats are connected to the mixing boxes
What is access flooring and what is it used to accommodate?
Access flooring is a false floor of individual panels raised above the structural floor with pedestals

It is commonly used to accommodate electrical, communication, and computer wiring. It CAN be used for some HVAC ductwork
In what application are chase-walls commonly used?
Between back-to-back commercial toilet rooms where extensive plumbing work and toilet carriers are required
What is an access door?
typically small steel doors with frames that are opened using a thumbturn or a key. If required, they are available as fire-rated assemblies
Study the minimum clearance of window coverings for exterior glazing
What is a slot air diffuser?
can be used when the appearance of the air distribution device needs to be minimized or when the available space does not allow for a square diffuser

finished opening of about 3-8"W. These diffusers are long and narrow
Study the key mechanical symbols on drawings
The device that controls the volume of air and its distribution in an HVAC system is called a
(a) duct (b) register (c) convector (d) grille
(b) register

A convector transfers heat from a hot water system to the air.
A grille may control the distribution of air but has no provisions for controlling the volume of air.
A duct simply directs the transfer of air from one point to another.
Which of the following structural systems could small ductwork MOST easily be placed within?
(a) open-web steel joist (b) beam and girder steel c) waffle slab (d) flat plate concrete
(d) flat plate concrete

A flat plate concrete structure consists of just a slab of concrete and columns making it possible to run ductwork in any direction and in any portion (except for the column locations) without interference from any structure.
what are diffusers, registers, and grilles?
Diffusers have directional fins at different angles (sometimes adjustable) to distribute the air throughout the space.

Registers (in the floor or wall) can be open, closed, or adjusted somewhere in-between.

Grilles often used for return air have no movable parts or slats for adjustment.

Note: on the exam, fill in the blank questions will have numerical answers only.
An air handler access panel should measure a minimum of:
2' x 2' (600 mm x 600 mm)
Which of the following requires flexible ducting that is connected to main ductwork:
(a) air handling unit
(b) supply air register
(c) sprinkler branch line
(d) return air grill
(b) supply air register

Supply air registers are often connected to the main ductwork with flexible ducting. This allows some adjustability in the exact location of an air register if its location conflicts with some other ceiling mounted item. The mechanical engineer should be consulted to determine how much the registers can be moved.
What type of system would be best for an open office plan so the heating and cooling for each workstation could be individually controlled?

all-air
air-water
all-water
radiant panel
An all-air system can be subdivided into as many individually controlled areas as needed.

Radiant panels could be used, but it would be awkward to locate them in the ceiling and the cost would be much higher than that of an all-air system.
Ventilation does all of the following EXCEPT?

remove odor
provides oxygen
increase evaporation and heat loss through convection
carry away contaminants
Ventilation refers to the process of replacing all or part of a space's air to control temperature and other factors. It is required to provide fresh oxygen and remove carbon dioxide, to remove odor and carry away contaminants.
It includes the circulation of air within a building's spaces as well as exchange of air to the exterior. Interiors can be maintained at the desired temperature by tempering the air in the space with heating and cooling methods.
Ventilation also is essential in introducing fresh air to replace air that can become stale when it is recirculated within a closed building or space. Inadequate ventilation can also produce what has been termed "sick building syndrome," as a result of concentrated indoor air pollutants such as volatile organic compounds (VOCs).
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