Ballast: Chapter 17 - Mechanical, Electrical, and Plumbing Systems Flashcards
Net-Zero Structure
One that only consumes as much energy as it produces on site through renewable means.
Natural Gas - Pros + Cons
Pros -
Most efficient fossil fuel
Clean burning
Relatively low in cost
Cons-
Not available in rural or remote areas
Price fluctuates
Heating value 1050 Btu/ft3
Propane
A type of gas used where natural gas is not available - stored in pressurized tanks
Heating value 2500 Btu/ft3
Oil
- Cost and availability depend on world and local market conditions.
- Must be stored in or near the building
- Produced in 6 grades (lower numbers are more refined/expensive)
- No. 2 fuel for residential and light commercial (heat value 137,000 Btu/gal)
- No. 4 and No. 5 fuel for large commercial (heat value 152,000 Btu/gal)
Electricity
- Easy and inexpensive to install
- Easy to control/flexible in zoning
- Cost can be disadvantageous due to “peak use” pricing
- Ideal for radiant heating/hydronic radiant
- Heating value 3413 Btu/kW
Steam
- Not a basic fuel
- Available in urban areas/campuses as a by-product of electricity generation
- Not used directly for heating; used to heat water for water and air heating systems and to drive absortion chillers
Heat Pumps
A device that reverses the travel of heat from warmer locations to cooler ones. Can provide heat in the winter and cooling in the summer.
Heating efficiency decreases as outside air temperature decreases - sometimes used with a solar system for better efficiency.
How does a heat pump function as an air conditioner?
- Evaporator absorbs heat from the inside air
- Warmed refrigerant moves to condenser
- Releases heat in the condenser to the outside air
- Cooled air moves back to evaporator, etc.
Name 5 natural energy sources
- Solar (active or passive) - okay for residential and light commercial
- Photovoltaic (PV) - still expensive and limited use
- Geothermal
- Wind
- Tidal
Degree Days
A unit to measure how much heating or cooling is needed in a particular location over the course of a year.
Found by taking the difference between a baseline indoor temp of 65 deg. and the average outside temperature for the day. Total sum of all daily values to determine annual degree days.
Approximate Efficiency of Natural Gas
70-80%
Approximate Efficiency of Propane
70-90%
Approximate Efficiency of No. 2 Oil
65-85%
Approximate Efficiency of Anthracite Coal
65-75%
Approximate Efficiency of Electricity
95-100%
What is a furnace?
Device which converts fuel to heat by burning fuel inside a combustion chamber
What are the three types of forced air furnaces?
- Upflow - return air supplied at bottom of unit and heated air is delivered out the top of the furnace and distributed through ductwork
- Downflow - opposite of upflow. Used in cases where ductwork is located in a basement or crawl space and furnace is on first floor
- Horizontal - used where headspace is limited
What is a boiler?
A device which uses fuel to create hot water or steam
What are the two main types of refrigeration?
- Compressive refrigeration
2. Absorption
What is compressive refrigeration?
Based on transfer of heat during liquefaction and evaporation of a refrigerant .
Gas releases heat as liquefied
Liquid absorbs heat as it vaporizes
Problematic Refrigerants
- Freon - contained CFCs
- CFCs - deplete the ozone layer. Now banned
- HFCs - okay for ozone, bad for CO2 production
- Other more environmentally friendly substances tend to be toxic (ammonia, sulfur dioxide)
What are the primary components of a compressive refrigeration system?
Compressor, Condensor, Evaporator
Absorption
Produces chilled water through the loss of heat when water evaporates in a closed loop system using a saltwater solution
Evaporative cooling
Only works in hot-arid climate
HVAC System: Direct Expansion (incremental unit)
Self contained unit that passes non-ducted air over an evaporator. Ventilation comes from outside which is good for indoor air quality.
Can be through wall types, roof mounted, or packaged
HVAC System: Variable Air Volume (VAV)
All-air system where
- air is heated or cooled as needed in a central plant and distributed to the building at a constant temp through one duct.
- Each zone has a thermostat which controls a damper to vary the flow of conditioned air to user’s needs
- Return air dampers regulate amount of fresh air intake (up to 100%)
- Not great for simultaneous heating and cooling loads
HVAC System: High Velocity Dual-Duct
- Two parallel ducts run to each space, one with hot air, one with cool air.
- Mixing box at each zone controlled by a thermostat
- Good for req’d simultaneous heating and cooling
- Inherently inefficient due to amount of ductwork and fans req’d
HVAC System: Reheat (Constant Volume)
Return air and fresh outdoor air are mixed for cooling and dehumidification
Reheating can be done with hot water or electricity
HVAC System: Multizone
Air is supplied to a central mixing unit with separate dampers to temper air being sent to different zones
HVAC System: All-Water
Uses a fan coil in each conditioned space. Fan coils are connected to water circuits or hot and chilled air. Efficient system
HVAC System: Air-Water
Central air system using local fan-coil units
Used where air cannot be recirculated bc of potential for contamination (such as hospitals and labs)
“Induction System”
HVAC System: Electric
Grid of wires to produce radiant heat is most common
Electric baseboard radiators are also common
Only economical where electricity is inexpensive
Direct Expansion Systems are used for:
Single Fam Residence
Constant Volume Single Duct systems are used for:
Auditoriums/Theaters Churches Hospitals Hotels/Motels Laboratories Single Fam Residence Shopping Centers
Variable Air Volume systems are used for:
Auditoriums/Theaters Churches Small commercial Laboratories Libraries Office Buildings Shopping Centers
Dual Duct High Velocity systems are used for:
Hospitals
Laboratories
Constant Volume Terminal Reheat systems are used for:
Hospitals
Laboratories
Multizone systems are used for:
Auditoriums/Theatres Churches Small Commercial Hospitals Libraries Office Buildings
All-Water systems are used for:
Small Commercial
Single Fam Residence
All-Water Induction systems are used for:
Hospitals
Office Buildings
Closed Loop Heat Pumps are used for:
Apartments
Hotels/Motels
Fan Coils are used for :
Apartments Hospitals Hotels/Motels Office Buildings Schools
Electric systems are used for:
Small commercial
Single Family Residence
What criteria do you use to select an appropriate HVAC system?
- Use profile of the building
- Outdoor air requirements
- Building Scale
- Control Needs
- Fuels Available
- Climatic Zone
- Flexibility
- Integration with the Building System (structural, etc)
- Economics
Name 5 of 12 systems that may require a dedicated exhaust system.
- Equipment/processes that throw off dust
- Equipment/processes that emit heat, odors, fumes, spray, gas, or smoke
- Hazardous mat’ls used in production
- Garages and car repair facilities
- Clothes dryers
- Domestic kitchen exhaust
- Commercial kitchen hoods
- Laboratories
- Dust + refuse conveying systems
- Sub-slab soil exhaust systems
- Smoke control systems
- Energy recovery ventilation
Define Nuisance
Legal term meaning that which is dangerous to human life or detrimental to health. Used in reference to exhaust air discharge locations
What percentage of the overall energy consumption of a building is HVAC?
40-60%
How are HVAC systems rated on energy efficiency?
- Annual fuel utilization efficiency
- Coefficient of performance
- Energy efficiency ratio
- Integrated part load value (IPLV)
- Seasonal energy efficiency ratio (SEER)
Economizer cycle
It is a mechanical system which uses outdoor air when it is cool enough to mix with recirculated indoor air
Dual Condenser Cooling
Refrigeration equipment with 2 condensers instead of one. If heat is needed, condenser A sends waste heat to fan coil units. If cooling is needed, condenser B sends heat to cooling towers.
Gas Fired Absorption Chillers
Does not rely on electricity or refrigerants. Not as efficient, and not necessarily cost effective
Solar Power Absorption Chillers
Efficient and sustainable - powered by hot water from solar collectors
Solar Powered Desiccant Chillers
Passes air over a desiccant which cools and dehumidifies the air
Direct Contact Water Heaters
Passes hot gases directly through water to heat it
Recuperative Gas Boilers
Recovers the heat in flue gases that would normally be discharged. Cools the flue gas enough to condensate, recovering both latent and sensible heat
Displacement Ventilation
Air distribution system in which supply air is dispensed at floor level and rises to return air grilles in the ceiling as it warms. Bc it is delivered closer to users, it doesn’t need to be cooled as much
Water-Loop Heat Pumps
Uses a series of heat pumps for different zones of a building. All pumps are part of the same piping system. When some zones are cooling, they dump heat into the system which helps with the heating zones and vice versa
Thermal Energy Storage
Uses water, ice, or rock beds to store excess heat or coolness for use at a later time.