Flashcards in Chapter 7 | Heating, Ventilation, and Air Conditioning Systems Deck (28)
What is natural air ventilation?
Air entering or leaving through an opening in the building
What are the disadvantages of natural air ventilation?
1. Limited control on rate
2. Cannot control temperature of incoming air
3. Limited control on contaminates entering the air
4. Limited impact on interior rooms
What is mechanical air ventilation?
Air being drawn in and exhausted from the facility using fans
What are the advantages of mechanical ventilation?
1. Can control the rate of air flow
2. Can direct through a ventilation system to condition air before it is introduced into the room
3. Can direct air anywhere inside the facility
What is a central ventilation system?
Single air handling system circulating air throughout the entire facility
What are the advantages and disadvantages of a central system?
1. Efficient system for large buildings
2. Prevents rooms from developing stale odors when unoccupied
1. If the system fails, the entire facility is without ventilation
2. If re-circulation is used, contaminates from one room could be spread throughout the entire building
What is a room ventilation system?
Each individual room has its own air handling system
What are the advantages and disadvantages of a room ventilation system?
1. If the system fails, only one room is affected
2. Contaminates are not shared between rooms
1. Initial costs are higher for large buildings
2. High maintenance costs
What is a zone ventilation system?
The building is divided into zones and each zone has its own system
What are the advantages and disadvantages of a zone ventilation system?
1. More efficient than rooms system
2. Failures only affect one zone, not the whole building
3. Contaminates are only shared within zones
4. Can be retrofitted into older buildings easier than a central system
1. Not as efficient as central systems
2. Failures affect more than one room
3. Contaminates are shared between zones
4. Higher installation cost than central
Can room heating/cooling be incorporated into a central- or zone-ventilation system?
Yes. By having central ventilation, the air will be constantly flowing through the room, keeping it from getting stale. By having individual heating/cooling, you don't waste energy by heating/cooling an unused room
What are ductless hoods?
Hoods that filter the air coming off the equipment then return it to the room
What are the advantages and disadvantages of ductless hoods?
1. Can be used in locations where it is not possible to run a duct to the exterior of the building
1. Cannot be used on gas equipment
2. Does not exhaust heat, moisture, or gases
Describe the four main types of filters
1. Dry filter
a. Standard dry: low pressure drop but doesn't remove much
b. Pleated filters: High pressure drop but removes everything; single pass filter
2. Water spray filter: removes dust, smoke, and odors. Humidifies and cools the air. Only used on exhaust hoods
3. Electronic filter: Removes smoke, odors, and dust; not a single pass filter; Low resistance to flow; extremely efficient; low operating cost; high installation costs.
4. Grease filter
a. Baffle filter
What is the problem with relying too much on air from the room to provide makeup air for kitchen hoods?
What are the three ways to provide makeup air? Which is most efficient?
1. Short circuit
2. Vents near but outside of the hood
3. Rear discharge - most efficient way to provide makeup air
What are the two types of commercial exhaust fans?
1. Upblast - Most popular. Keeps discharge from running down the roof.
What are the two types of grease filters?
1. Baffle (standard) filter
a. Air is rushed through the filter at 250-350 ft/min. As air moves around the curve in the filter, centrifugal forces cause the grease to be thrown against the filter, removing it form the air
a. Air is rushed through the filter at 1000-1200 ft/min. High centrifugal forces remove more grease. More efficient.
Why is it important to maintain indoor air quality?
1. To prevent sick building syndrome
What is the leading cause of indoor air quality problems?
Why is the ideal temperature setting higher in the summer than in the winter?
1. People wear fewer clothes in the summer
2. People get acclimated to the warmer temperatures
3. Heat transfer - if the inside temp is closer to the outside temp, it costs less to maintain the building
How does an adobe keep the interior at a comfortable temperature without using an air conditioning system?
The thick mud walls soak up the sun in the daytime while keeping the inside cool. At night, the warmth in the walls keeps the interior warm
What are the 7 components of an air-conditioning system?
1. Damper - controls the rate of air flow
2. Filter - removes unwanted particles from the air
3. Preheater - Makes the air easier to humidify
4. Precooler - Makes the air easier to dehumidify
5. Humidifier - adds moisture to the air
6. Dehumidifier - removes moisture from the air
7. Fan - Moves air through the system and the entire building
Why is it important for filters to be located before the preheater, precooler, humidifier, dehumidifier, and fan?
Fouling makes preheater non-efficient, makes mud in the humidifier and dehumidifier and causes fires in the fan
Why is it important that the preheater be installed before the humidifier?
Warm air holds more moisture
Why is it important that the precooler be installed before the dehumidifier?
Cooler air is more energy efficient to dehumidify
What are the advantages and disadvantages of the two types of fans?
a. Works well under constant loads
a. Works well under varying loads