Systems Integration Flashcards
In HVAC design, what are the three fundamental types of systems, as far as socpe, and some examples of each?
Local System
Serving a single zone, either for a small building or a discrete portion of a larger building. Uses the least in-building space.
EX: a residential furnace, a window-mounted AC unit
Centralized System
One system serving several different zones. Boilers, chillers, pumps, and/or air handling units supply air, water, or hydronic fluid to several zones. Uses the most in-building space.
EX: commercial or industrial buildings of moderate to large size
District System
A plant provides hot or cold fluid to several buildings, each of which have their own smaller utilization and distribution system. Uses a moderate amount of in-building space (since generation occurs elsewhere).
EX: steam system in city, steam or chiller system on a college or business campus
What are the five general types of HVAC system, as far as method of delivery, and some aspects of each?
All-Air System
- Air is pushed throughout the zone(s) and returned to the generation point with ducts.
- Takes up the most space because of volume of air that must be handled.
- Excellent humidity control
All-Water System
- Water (hydronic fluid) is pushed throughout the zone(s) and returned within the same closed loop. Direct heat transfer at each radiator or fan-coil unit, no ducting.
- Takes the least amount of space, because only water (low volume) must be moved.
- No (very poor) humidity control
Air-Water System
- Pre-conditioned air is provided to each zone, but most heat transfer takes place at individual fan coil units.
- Return air can be exhausted (if necessary per program (EG, laboratory), or can be returned through plenums or space.
- Takes a moderate amount of space.
- Moderate-to-excellent humidity control (depending on configuration)
All-Electric System
- Heating through ceiling wire or baseboard devices.
- No humidity control
Direct Expansion System
- Package unit performs generation, heat transfer, and air handling
- Poor humidity control
What some the general space requirements for mechanical rooms for the three types of central HVAC system?
Mechanical Room (% of total building area):
- All-Air: 3-10%
- All-Water: 1-3%
- Air-Water: 3-10%
- The range depends on the building use.
- Low end: residential
- Medium: buisness, commercial, educational, assembly
- High end: labs, institutional, some types of industrial*
Cooling Towers: 0.2-1% of total building area
Boiler and chillers rooms: minimum 12-18’ height
What are some of the common components of an air-handling system? (whether part of a package unit, off-the-shelf products, or custom fabricated)
- Fan
- Filters
- Humidifier
- Pre-heat coils
- Return air port
- Exhaust port
- Outside air / make-up air ducts
- Economizer
- Control dampers
- Mixing box
What are the primary concerns with respect to forced-air pressure in ducted HVAC system?
The amount of pressure needed to make the air move through a duct / duct system is the “static pressure”, measured in inches of water.
The statis pressure must be higher the:
- longer the length of duct
- more turns
- more fittings / transfer openings
- smaller the duct cross-section
Larger ducts need less static pressure but requires more space
Higher pressure means stronger fans (higher intial- and operating-costs) and more noise.
What are some general code requirements on plenums?
If a plenm is used for return-air, then most code require that is have additional protections.
Usually, no combustible matirals may be in this space. The biggest impact of this is that electrical wiring must be in conduit.
Sometimes the plenum must be sub-divided to prevent the spread of fire. This is usually done by extending the interior partitions to the deck.
What are some general rules for placement of thermostats?
- Should not be on exterior walls
- Should not be placed near heat sources or heat sinks
- Normally at 48”, but should be coordinated with switches in the room
- Must comply with accessibility reach ranges; mainly means that if there is an obstruction that extends 20-25” off the wall, the thermostat must be below 44”
What is Static Head and what is its relationship to PSI?
Static head is the current water pressure at a given point in system. It is expressed in vertical linear feet of water.
1ft = 0.433 PSI 1PSI = 2.3ft
Friction in the plumbing system, which is greater the more turns in the piping, reduces static head.
What are some general design principles of up-feed plumbing systems?
The maximum height of a building using an up-feed system is about 40-60ft (depending on local water pressure)
What are some general design principles for a down-feed plumbing system?
The maximum height of a system using a down-feed system is about 140ft, since the maximum allowable pressure for most types of fixtures is 45-60 PSI. For heights greater than that, a pressure reducing valve or multiple storage tanks for different zones must be used.
Fixtures near the top of the down-feed system need to be low enough below the tank to received enough minimum pressure.
What are the three general types of plumbing feed systems?
Up-feed
Water pressure from the municipality or local system servers all fixtures in the system
Down-feed
A pump fills tank(s) near the top of the system(s) than then supply gravity-pressure water to all the fixtures in that zone of the system
Direct up-feed pumping system
Also called a “tankless” system. Several pumps supply water pressure to the entire system/zone, and a sensor activates one or more pumps to adjust for current pressure demand
What are three common types of plumbing valves?
Gate Valve
A plunging wedge cuts of water flow. Direct linear flow has little pressure loss to friction, but has a pretty much ‘all on’ or ‘all off’ function.
Globe Valve
A plunging stopper comes down on a gate that is perpendicular to water flow. Has high pressure loss to friction but allows for better moderation of flow.
Check Valve
A flap only allows water to flow in one direction.
What are the two general methods of reducing the use of potable water for irrigation and some aspects of each?
Use Native Plants
In landscaping, make as many plants as possible species that are native to the area, which are adapted to the amount of rainfall.
Design Irrigation Efficiently
- use irrigation timers so that irrigpation can be done in the mornings and evenings, when loss to evaporation will be the least
- use rain sensors to limit irrigation when it is not needed
- use tensiometers to limit irrigation when the soil is already moist enough
- use drip-irrigation system for small trees and shrubs
What are some common water temperature requirements for different uses?
95°F - Theraputic baths
105°F - handwashing
110°F - showers and bathing
140°F - residential laundry and dishwashing
180°F - commercial laundries, sanitizing dishwashing
What are the primary aspects of blackwater and greywater?
Blackwater is any sanitary waste water that contains human waste (such as from toilets and urinals)
Greywater is any sanitary waste water that does not contain human waste (such as from dishwashers, sinks, laundries, and showers). Some traces of human waste may be present from showers and laundries.
Greywater may be re-used for certain things (such as irrigation or toilet flushing) with moderate to minor treatment.
