Week 9 - Innovation and discovery, IEQ, ventilation, and thermal comfort Flashcards
What are the main factors in indoor environmental quality (IEQ)?
- Visual comfort
- Aural comfort
- Indoor air quality
- Thermal comfort
What are the goals and strategies of IEQ?
- Minimize risk of building-related health problems
- Maintain high-quality indoor environments
- Big part of HKBEAM assessment
Strategies——————– - Control pollutants
- Introduce daylight and views
- Provide occupants with controls
- Acoustic and thermal comfort
How does ventillation play a part in IEQ?
- Clean air, stale air removed
- Can be natural or mechanical means of ventilating
Natural——————- - Intentionally provided openings
Mechanical —————————- - Driven by mechanical fans
- Indoor air distribution scheme with mixing ventilation, displacement ventilation, stratum ventilation
What is mixing ventilation?
- Air delivered at high velocity outisde occupied zone (like from ceiling)
- Generates excess presure –> inflow and entrainment of room air towards jet
How does displacement ventilation work?
- low-velocity stream of air near floow to displace stale air up twaords ceiling
- allows higher evaporator tmp
- higher average room air temperature
—> example: displacement ventilation system at EMSD system
How does stratum ventilation work?
- Develope for elevated indoor temperature
- Leveled at where the people
- IAQ in the breathing zone is most important
- Head level needs more cooling
- Includes air temperature and movement (based on ASHRAE Standard)
- On average 40% saving using this method (compared to about 20% of other methods)
What are the 9 factors that contribute to energy saving of stratum ventilation?
- Neutral temp of 27 degrees –> lower latent load – lower temp than other systems
- Smaller temp difference betwen outdoors and indoors
- Smaller enthalpy (total energy content of a system) difference between indoor and outdoors –> lower ventilation load
- Longer free cooling period
- Higher ventilation effectiveness
- Reverse temperature graddient –> no over-cooling of lower zone (cuz heat rises)
- Elevated supply air temperature
- Lower cooling capacity –> smaller and less powerful fans and devices
- Shorter pull down period (time required to change temp)
Other benefits of stratum ventilation?
- Smaller mechanical plant and ductwork
- less space that aircon takes up
- scaffolding becomes unnecessary
- substantially lower year-round energy consumption
- initial cost is lower
- operation cost is lower
- carbon footprint lifecycle is smaller
What are some Unique Characteristic of Stratum Ventilation Technology?
- all new and all old tech
- all new: innovative concept
- all old: necessary components already exist, easy to adapt and hard to fail
What are the factors influencing Factors Influencing Thermal Comfort?
- air temp
- relative humidity
- air velocity
- mean radiant temperature
- metabolic rate
- clothing insulation
What is the Predicted Mean Vote (PMV) Index?
- Predicts mean response of a large group of people according to ASHRAE thermal sensational scale
- Activity level (metabolic rate) – type of physical activity involved, heat energy released from human body
- Clothing – affect skin temp and saturated vapor pressure at skin ruface – basically has to do with energy exchange between human body and environment
- Air temp (dry bulb temperature) – temp of air WITHOUT impact of moisture or radiation
- Relative humidity –Affects evaporative heat loss and skin wetness (40 - 70% is considered comf)
- Relative air velocity – increase in air velocity increases heat dissipation from skin, lower air velocity is preferred
What is ASHRAE?
- American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
- Global professional association for advancing heating, ventilation, aircon, and refrigeration
- Have a developed standard for HVAC%=&R systems
- ASHRAE Standard 55-2013 – allows elevated air movement to offset and cool the air
What is the equation of energy balance between the human body and environment?
S = M - W - E - Q
S = rate of heat storage of human body, W /m 2
M = metabolic rate of human body, W /m 2
W = mechanical work produced by human body, W /m 2
E = rate of total evaporative loss, W /m 2
Q = total rate of heat loss from skin (dry heat exchange), W /m 2
S = 0: therman neutrality in body
What is evaporative loss?
- Convective or sensible respiration heat loss
- Latent respiration heat loss
- Heat loss due to regulatory sweating
- Evaporative Heat loss by skin diffusion
- Respired vapor loss
- Evaporated heat loss from skinn surface
What is dry heat exchange?
- Convective and radiative heat transfer
- No water involved
- Either +ve or -ve
- Transfer of heat from one place to another by movement of fluids
