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Cards In This Set
| Front | Back |
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On average what is residental use of HVAC. Commercial use?
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13% residental
20% commercial as high as 30 to 50% |
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What are typical design ranges for temp & RH?
ventilation? what codes? |
75F dry bulb
40-60% relative humidity ASHRAE 62, 1999, 2001, 62.1-2004 20 CFM outside air per person (now 17 CFM) or co2 less than 1000ppm |
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What are three types of temperature control strategies?
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Constant volume - vary temp of supply air but keep rate constant
Variable air volume (VAV) - vary air flow rate while keeping supply temp constant Variable Volume Reheat System - vary both temp & flow |
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What are ways of relative humidity control?
What's an issue with AC control related to this? |
Humidification - if air too dry
Dehumidification - if air too wet AC systems typically over-cool and then may have to reheat air, which requires additional energy |
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How much energy is req'd per pound of water?
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1000 BTU
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Four types of primary equipment
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Chillers
Boilers Furnaces Direct Expansion Systems |
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What are the six secondary systems?
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Single duct, single zone
Single duct, terminal reheat Multizone system dual duct system Single duct, VAV system (most common) Fan coil system |
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Do you want a positive or negative pressure on a single duct system and why?
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Positive pressure b/c don't want rogue air able to get in.
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What are two types of economizers?
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Temperature or Dry Bulb economizers - doesn't account for humidity levels. (if it's 55F & 80%RH may not be good)
Enthalpy based economized will look at the overall btu content of the air |
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How does a single duct, single zone system operate?
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Takes some air & mixes with outside air, goes thru economizer & then thru fan which operates at a static to overcome all downstream drops
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How does a terminal reheat system different for SD, SZ?
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At the end of ductwork, each zone has own coil & thermostat will control how much goes into coil.
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Where does mixing occur in dual duct system?
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Two ducts throughout, thermostat @ zone will determine level of mixing at the mixing box at the terminal.
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What is the most common type of HVAC in large commerical buildings?
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Single duct, VAV system - high efficient with use of VFD on supply air fan. Has local terminal box in the zone.
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How much heating is the same as one ton of A/C?
one ton-hr? |
12,000 BTU/hr
12,000 BTU |
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Where are fan coil systems typically used?
How do they operate? |
Schools, hospitals, etc
Hot or cold air is sent thru the coil and the radiator works by convective heat transfer |
