Determining Mechanical, Plumbing, and Electrical Systems Flashcards
Human comfort is based on which 8 environmental factors?
- temperature
- humidity
- air movement
- temperature radiation to and from surrounding surfaces
- air quality
- sound
- vibration
- light
What are the 3 ways a body loses heat? When does each occur?
- convection = transfer of heat through movement of liquid or gas. Occurs when the air temperature surrounding a person is lower than their body temperature
- radiation = the transfer of heat through electromagnetic waves from one surface to a colder surface.
- evaporation = occurs when moisture change to a vapor as a person breathes or perspires
Thermal comfort depends primarily on which 6 environmental factors?
- air temperature
- air movement
- humidity
- ventilation
- surface temperature
- clothing
Which is always lower, the dry bulb or wet bulb temperature?
What does a large difference between dry bulb and wet bulb temperatures indicate?
What does it mean when dry bulb and wet bulb temperatures are the same?
wet bulb is always lower than dry bulb
large difference = low relative humidity
equal = air is at 100% humidity
What is relative humidity?
The ratio of moisture in the air to total moisture the air could hold
What is the difference between emissivity and emittance?
emissivity = the measure of an object’s ability to absorb and radiate heat
emittance = ratio of radiation emitted by a given object to that by a black object at the same temperature
What is 1 clo?
1 clo = the amount of thermal insulation provided by the typical business suit
What is the “effective temperature”?
A value that combines air temperature, humidity, and air movement.
What are 2 common methods to show the various environmental factors for human comfort?
- comfort chart
2. psychrometric chart
What does a psychrometric chart do?
What are the factors in a psychrometric chart?
Give a dry bulb temperature and specific humidity, how do you find the:
Dew point?
Wet bulb?
Max humidty? Relative humidity?
It helps calculate how much heat and moisture need to be added or removed by an HVAC system for comfort.
Horizontal axis = dry bulb temperature
Vertical axis = specific humidity (grains)
Left curve = 100% humidity
horizontally left from dry bulb and specific humidity gives you dew point
diagonal up/left from dry bulb and specific humidity gives you wet bulb
straight up and then straight right from dry bulb gives you max humidity
relative humidity = specific humidity / max humidity
What is the R-value of a material?
Resistance = the number of hours needed for 1 Btu to pass through a material of a given thickness when the temperature differential is 1 deg F.
What is is the U-value of a material?
Conductance = the rate at which heat passes through 1 sf of a material of a given thickness when the temperature differential is 1 deg F.
How do you calculate the amount of heat loss through unit of areas of a building material or assembly?
Q = (U-value) x (Area) x (change in temperature from inside/outside)
this formula is provided in the exam resources
Where should the vapor barrier go?
On the warm side of the insulation. So, if it’s hotter outside than inside, the vapor barrier should go on the exterior side of insulation. If it’s colder outside than inside, the vapor barrier should go on the interior side of the insulation.
How do you calculate heat loss through air infiltration?
Q = (volume of air lost in cubic feet per min)x(1.08)x(change in temperature from inside/outside)
this formula is provided in the exam resources
What is the difference between sensible and latent heat?
sensible heat = heat exchange through temperature
latent heat = heat exchange without temperature change, through gas or liquid
What are the 6 main options for fuel?
- natural gas
- oil
- electricity
- steam
- heat pumps
- natural energy sources
What are 2 types of refrigeration processes that produced chilled water or air? What is an essential difference between them?
- compressive refrigeration = uses a compressor to deliver the ammonia solution at high pressure to the condenser, where it releases heat.
- refrigeration by absorption = uses an absorber/generator loop to deliver the ammonia solution at high pressure to the condenser, where it releases heat.
Essential difference: compressive uses mechanics, whereas absorption uses laws of chemistry and physics. Also, compressor requires more energy than the absorbor/generator loop
What are the 3 components to compressive refrigeration?
- compressor = refrigerant is compressed, turning to a liquid
- condenser = liquid refrigerant is condensed and releases latent heat
- evaporator = refrigerant evaporates into a gas and draws heat from its surrounding
Which 2 types of refrigerant are not used anymore? Which is used instead?
Freon
CFCs
= deplete the ozone layer
HCFCs have replaced CFCs = less ozone depletion
What is evaporative cooling?
In which climates is it appropriate to use?
What is a benefit over a refrigeration cooling system?
Water is dropped over pads of fin tubs through which outdoor air or water circulates. As the free water evaporates, it absorbs heat from the outdoor air/water. This cools the outdoor air/water, which is then used to cool the building.
Only works in hot-arid climates where outdoor air has low enough humidity to allow the moistened air to evaporate.
It can be more economical and easier to install than a refrigeration cooling system
What are the 5 broad categories of HVAC systems?
- Direct expansion (DX) Systems
- All-air systems
- All-water systems
- Air-water systems
- Electric systems
What does the direct expansion (DX) system do?
It is the simplest type of HVAC system in which a self-contained unit cools non-ducted fresh air with a refrigerant vapor expansion and compression cycle. The cool air is then discharged into the room.
- Intake comes directly from outside -> improved IAQ
- With the addition of a heat coil, can provide heating as well.
What are 5 types of all-air systems?
- Constant-Volume Single-Duct System
- Variable Air Volume (VAV) System
- High-Velocity Dual-Duct System
- Variable Refrigerant Flow (VRF) System
- Multizone System
What is a constant-volume single-duct system?
- central unit?
- independent control?
- boiler/chiller or heat pump or refrigerant?
- where it is most often used?
the simplest type of all-air system in which air is heated/cooled in a central furnace/air conditioner and is distributed through ductwork at a constant volume.
- central unit
- central thermostat = no independent control
- boiler/chiller to heat/cool air
- often used in residential and small commercial
What is a variable air volume (VAV) system?
- central unit?
- independent control?
- boiler/chiller or heat pump or refrigerant?
- where it is most often used?
- what is 1 negative?
Air is heated/cooled in a central plant and distributed through a single duct at a constant temperature.
- central plant
- individual zone control but not simultaneous H/C
- boiler/chiller
- efficient air conditioning large internal load dominated buildings.
- Limited in extreme simultaneous heat/cooling demands
What is a high-velocity dual-duct system?
- central unit?
- independent control?
- boiler/chiller or heat pump or refrigerant?
- where it is most often used?
- what are 3 negatives?
2 parallel ducts run to each space, one carrying hot air and the other cold air. The two streams of hot/cool air are joined in a mixing box in proportions to suit the temperature requirements of the space.
- central distribution unit
- individual zone controls = thermostat controls the mixing box for each space
- boiler/chiller
- best for buildings that need varying simultaneous heating/cooling requirements.
1. - inherently inefficient since both hot air and cold air are supplied at all times
2. - high velocity = higher energy for more powerful fans and higher noise with in ductwork
3. - high quantity of ductwork = higher cost
What is a similarity between a VAV and high-velocity dual duct system? Difference?
They both provide heating/cooling with boiler/chillers with individual zone control.
VAV cannot provide large simultaneous differences in heating/cooling since it has a single duct, but high-velocity dual duct can. VAV is better for large internal load dominated buildings. high-velocity dual duct is better for buildings that need varying simultaneous heating/cooling requirements.
What is a variable refrigerant flow (VRF) system?
- central unit?
- independent control?
- boiler/chiller or heat pump or refrigerant?
- where it is most often used?
A single compressor and condenser unit is located outdoors and connects to multiple evaporators located in different zones/rooms. Reduces power consumption by operator compressor and evaporators at varying speeds to precisely meet the load in each zone.
- individual zone control through individual evaporators
- uses refrigerant. Can also be designed to use a heat pump or heat recovery to reduce power consumption.
- best for buildings with varying heating/cooling loads and different zones:
- office buildings
- hotels
- schools
- multifamily residential
What is a multi-zone system?
- central unit?
- independent control?
- boiler/chiller or heat pump or refrigerant?
- where it is most often used?
Supplies air to a central mixing unit where separate heating (coiler) and cooler (chiller) coils product separate hot/cold air streams. Hot/cold air streams are mixed with dampers controlled by zone thermostats and delivered to the zones.
Best used for medium sized buildings that needs various heat/cooling in different zones, but where each floor is one with 1 central mixing unit/floor.
What is an all-water system?
- central unit?
- independent control?
- boiler/chiller or heat pump or refrigerant?
- where it is most often used?
uses a fan coil (boiler/chiller) in each conditioned space to heat/cool water.
- individual controls = thermostat in each room regulates how much water flows through the coils
- most often used in dry/arid locations = It is an efficient way to transfer heat and is easily controlled, but cannot control humidity.
What are the 3 types of all-water systems?
two-pipe = one supply pipe for both hot and cold and one return pipe three-pipe = two supply pipes for hot and cold and one return four-pipe = one supply/return circuit for hot and another for cold
What is an air-water system?
- central unit?
- independent control?
- boiler/chiller or heat pump or refrigerant?
- where it is most often used?
a central air system provides humidity control and ventilation air to spaces, with the majority of heating/cooling provided by fan coil units in each space for independent control. Supply air is 100% fresh and return air is completely exhausted to exterior.
- often used when return air cannot return to the system due to potential contamination (like laboratories or hospitals)
What are two types of air/water systems?
- air-water induction system = air is supplied to an induction unit (instead of coils) in a room/zone, where air is heated/cooled as needed
- fan coil with supplementary air = fan coiled unit provides heating/cooling, but separate supplementary air supply provides humidity control and ventilation
How does an electric heating system work?
most commonly a grid of wires in the ceiling of a room that provide radiant heating. Can also baseboard or floors.
- individual room control
- no space required for ductwork or piping
Determining an HVAC system for a building depends on which 10 interrelated variables?
- use profile of the building
- building scale
- control needs
- fuels available
- climatic zones
- flexibility
- integration with building systems
8 integration with alternate energy sources - economics
- energy efficiency
Does an all-water system or an all-air system have smaller ductwork?
An all-water system has smaller ductwork.
What are 4 techniques to reduce reliance on HVAC?
- mechanical system components
- heat transfer methods
- building automation systems
- building commissioning
What is an economizer cycle?
A mechanical system component that can reduce reliance on HVAC.
It uses outdoor air when it is cool enough to mix with recirculated indoor air to save energy for internal load buildings that need AC even in cool months. Useful at 60 deg F.
What is dual condenser cooling?
A mechanical system component that can reduce reliance on HVAC.
It is a refrigeration equipment that uses two condensers instead of one (can also have two chillers):
- heat recovery condenser = used when heat is needed
- heat rejection condenser = used when heat is not needed
It is efficient because the system can operate using the best condenser or chiller with the best size for the load.
What is gas-fired absorption cooling?
A mechanical system component that can reduce reliance on HVAC.
Absorption chillers are powered by gas instead of electricity or refrigerants. Not as efficiency as electric chillers, so best used in a place where electricity is expensive.
What is solar powered absorption cooling?
A mechanical system component that can reduce reliance on HVAC.
Absorption chillers can be made more effective if powered by hot water from solar collectors.
What is solar powered desiccant cooling?
A mechanical system component that can reduce reliance on HVAC.
Uses desiccants to dehumidify and cool air by evaporative cooling.
What are direct-contact water heaters?
A mechanical system component that can reduce reliance on HVAC.
It passes hot gases directly through water to heat it. Very efficient but very costly. Best used when there is continuous demand for water (food processing, laundry, industrial).
What are recuperative gas boilers?
A mechanical system component that can reduce reliance on HVAC.
They recover the heat from flue gases that would be otherwise exhausted and use them to preheat water or air.
What is displacement ventilation?
A mechanical system component that can reduce reliance on HVAC.
An air distribution system where supply air is dispensed at the floor level and exhausts through the ceiling as it warms and rises naturally. Air does not need to be cooled so much.
Required underfloor ductwork, so an extra 12” in floor-to-floor height. Best for new construction.
What are water loop heat pumps? When are they most efficient? In what type of buildings should they NOT be used?
A mechanical system component that can reduce reliance on HVAC.
A series of heat pumps in different zones in the building are all connected to a piping system of circulating water. When some zones are cooling others are heating, and heat is transferred between them. Only when all zones are operating at the same temperature does the water need to be heated or cooled.
Most efficient when there are simultaneous heating/cooling needs.
Not appropriate for buildings in small cooling loads.
What is thermal energy storage?
A mechanical system component that can reduce reliance on HVAC.
Uses water, ice, or rock beds to store extra heating or cooling until it’s needed. Can reduce how much the building needs to be heated or cooled later.
What is the general concept of “heat exchange”?
Taking heat from where it’s not wanted to where it is wanted.
What are Energy Recovery Ventilators (ERVs)?
In what climates is it most effective?
In what types of buildings is it most effective?
In what types of buildings is it prohibited?
An air-to-air heat exchanger that reclaims waste energy from the exhaust airstream and uses it to condition incoming fresh air.
Most effective in very cold, hot, or humid climates where the temperature differential between outside/inside is high. Not as efficient in temperate climates.
Most effective in buildings with continuous occupancy, like hospitals or hotels.
Prohibited in hazardous exhaust systems.
What are 3 conditions for an ERV?
- exhaust and intake must be located as far away as possible
- exhaust air containing excess moisture, grease, or other contaminated must be separated from the heat exchange air
- in cold months, a defroster may be needed to keep exhaust air from freezing
What are 3 common devices to facilitate heat exchange in an ERV?
- flat-plate heat recovery units = a flat plate separating the incoming air and exhaust air facilitates the heat exchange of sensible heat only. No humidity control.
- energy transfer wheels = a heat exchanger wheel with small openings filled with a desiccant absorbs moisture and transfers heat between intake/exhaust. Helps control humidity.
- heat pipes = refrigerant and a condenser/evaporator exchange sensible heat between cool intake and hot exhaust air. Intake and exhaust can be adjacent.
What is a water-to-water heat exchanger?
What is its main advantage?
In what type of building is it commonly used?
Uses water or other liquid in coils to transfer heat between intake/exhaust.
Main advantage = intake and exhaust do not need to be adjacent.
Commonly used in large buildings
What are extract-air windows?
A type of heat exchange in which air circulates between a double pane insulated glass and another layer of glass on the interior side. In the winter, air warms the glass and in summer air cools the glass.
It can eliminate the need for separate perimeter heating/cooling.
What are chilled beams?
A ceiling mounted unit that uses water to provide heating and cooling.
What are 3 types of chilled beams?
- passive chilled beam system = uses natural convection. Warm air rises, is cooled by the unit, then sinks back down. Separate ventilation ducts and humity controls are required.
- active chilled beam system = heats or cools fresh air and then forces it into the room.
- multi service chilled beam system = combines active chilled beam system with other building systems like sprinklers, lighting, data cabling, etc.
What are building automation systems (BAS)?
a computer-based integration system used to monitor and control building systems. They contain energy management systems (EMS) to help with energy conservation.
What is the basic material of an electrical system?
A conductor. Sizes range from:
Smallest = AWG size 16 gage
larger = AWG size 4/0 gage
Even larger = MCM sizes = 250, 300, 400, 500
What are wires?
What is a cable?
conductors no. 8 AWA and smaller
a single insulated conductor no. 6 AWA or larger OR several conductors assembled in a single unit
What are the 2 most common conductors?
- copper = more cost effective in small and medium-size wire and cable
- aluminum = requires special care so limited to primary circuits installed by skilled workers
When must conductors be placed in conduit?
for commercial or large residential construction
What are 2 common forms of electrical energy used in buildings?
- AC (alternating current) = most common
2. DC (direct current) = used in some types of elevator motors and for low-voltage applications
What are the 4 types of voltage a building may require?
- 120/240 V single-phase, three-wire system = common for SFR and small buildings
- 120/208 V, three phase, four-wire system = common for larger buildings
- 277/480 V, three-phase, four wire system = same as 120/208 system, except with higher voltage
- 2400/4160 V, three-phase, four-wire system = used by very large commercial buildings and factor with a lot of machinery
At which voltage does the building owner need to provide at transformer?
at 120/280 V or higher. At 120/240 it is provided by the utility company.
Why is metering required? Where is the meter located?
Metering is provided at a building’s service entrance to allow the utility company to charge for energy use.
What is a switchgear?
a central electrical distribution center required in large buildings to distribute power to individual panel boards and then to individual branch circuits for lighting, power, motor, etc.
What are 3 types of protection for circuits?
- grounding =
- ground-fault circuit interrupter (GFCI)
- arc-fault circuit interrupter (AFCI)
What is a ground-fault circuit interrupter (GFCI)? Where is it required?
= protects from small leaks unnoticed by the circuit breaker by disconnecting from power if there is a leak.
Required in bathrooms, kitchens, laundry rooms, and outside .
What is an arc-fault circuit interrupter (AFCI)?
Where is it required?
de-energizes unit when an arc fault is detected.
required in dining rooms, living rooms, libraries, dens, hallways, etc .
What are 3 automatic lighting controllers needed for energy conservation?
- time-of-day controller = turns of power at specific times
- occupant sensor
- daylight compensation control
What is the difference between emergency power and standby power?
emergency power is required for buildings where life safety is affected by lack of power. Powered by generators or batteries. Power/electrical system is totally separate from rest of building.
standby power provides electricity for building functions the building owner needs to avoid interruption of business. Power/electrical system can be integrated with other building components.
What are the 2 most common water supplies for cities?
- groundwater = water seeps into ground and forms a water table that can be tapped into by drilling
- surface water = rain and snow that run off into rivers and lakes
What are 4 common groups of water treatment? What’s are 2 other treatments?
- pretreatment = removes larger particles
- filtration = removes smaller particles, bacteria, viruses
- demineralization = removes dissolved liquids/minerals that cause hard water
- disinfection = destroyed microorganisms that cause disease in humans
- distillation = often used on seawater. Water is boiled down and vapors are captured, resulting in very clean water.
- oxidation/aeration = improves color or taste
What are 4 water treatment steps for municipal water supply?
- coagulation/flocculation
- filtered and treated with chlorine/sim
- aerated
- treatments to adjust pH level
then piped through water mains at 50 psi
What is one of the first tasks in a building project with regards to water supply?
Why is it important that this be done early?
Determine the location of the public water main, its size, its pressure, and the cost for tapping it. Get this info from the local water company.
Costs of extending water mains can be significant, so need to know early.
Open-loop or direct solar water heating system
= water used in the building is the same water that is heated in the solar collectors
Simple and highly efficient, but subject to freezing so must use some type of drainage system
Closed-loop or indirect solar water heating system
= a separate fluid is used to collect heat, which is then transferred to the domestic hot water
Easier to protect from freezing since fluid contains anti-freeze
Requires a heat exchanger, which reduces efficiency
Fluid can either be pumped passively (gravity) or actively (pumps)
Batch system
= a passive direct/open-loop solar heating system where water is heated directly in a black-painted tank inside a glazed box.
Simple but subject to freezing and nighttime heat loss
Thermosiphon system
= passive open-loop solar heating system that relies on the natural movement of heated water
Storage tanks located above the collectors
Keep piping simple to avoid pipe friction
Subject to freezing
Can use a variation of this system that is a passive closed-loop system with antifreeze fluid
Closed-loop active system
= solar heating in which liquid with antifreeze is circulated by pumps through solar collects and uses a heat exchanger to heat domestic water
Loss of energy due to heat exchanger
One of the most common types for residential and commercial
Flexible and provides control
Drain-down system
= a direct, open loop active solar heating system that automatically drains water from collectors when outside temperature is near freezing
Best for climates with mild winters so draining does not happen frequently
Drain-back system
= closed loop, indirect active solar heating system that uses water as the heat-collector fluid. Heated water is pumped to a heat exchange where a coil of domestic water is heated.
When the pump is off, the heat collector fluid drains out of the properly sloped collectors and pipe, leaving them empty and protected from freezing.
Phase change system
= a solar heating system that uses phase change materials as the collector fluid. Phase change materials store large amounts of both latent and sensible heat.
Water pressure increases in proportion to _____
depth (the taller the column of water, the more pressure it exerts)
What are 2 primary types of water supply systems?
How do you choose between the two?
- Upfeed system = uses pressure in the water main to directly supply the fixtures
Limited in height to 40 ft to 60 ft - Downfeed system = water from the main is pumped to storage tanks near the top of the building and flows to the fixtures by gravity
The pressure at any fixture can be determined by its vertical distance from the storage tank (4.33 psi/1ft of height)
Tank location may be driven by pressure needed and therefore vertical distance required) by fixtures near the top of the building
Limited in height to 138 ft. Taller structures require pressure-reducing valves
Choosing between the 2 is determined by a building’s height and its fixture pressure needs
Main idea that the architect should know for plumbing design?
= after the pressure losses are deducted from the available pressure at the water main, there must still be adequate pressure at the most remote fixture.
You get total pressure at water main from the local water company
Calculate pressure loss from rises in elevation by multiplying total rise in feet by 0.433 psi/ftt
Include pressure losses through piping and water meter (trial and error)
Pressure loss in pipes depends on diameter of the pipe and flow rate and is due to friction in the pipe.
What is Demand load?
= maximum possible flow = flow rate that would be needed if every fixture in the system were used at the same time
Can be found by adding up all the load values for every fixture
