{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Lecture-1Systems - Energy Efficient Heating 1 Waste Waste...

Info icon This preview shows pages 1–12. Sign up to view the full content.

View Full Document Right Arrow Icon
11/24/2009 1 Energy Efficient Heating
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
11/24/2009 2 Waste of heat in buildings results from: Poorly designed and insulated heating systems x The room might have a high ceiling, like a church, allowing all the heated air to concentrate at the top not warming the occupants at floor level x The pipes might not be well insulated, allowing heating in undesired areas
Image of page 2
11/24/2009 3 Poorly designed and insulated building envelopes x If poorly insulated, heat escapes by conduction to the outside x If the envelope is not well sealed heated air will travel through cracks around doors and window frames Poorly commissioned and maintained boiler plant x Heat meant to be warming water might be lost up the flue with combustion gases Poor controls x If the system is old, its controls will be inadequate Poor operating practices
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
11/24/2009 4 For best heating system in buildings: The building fabric and the mechanical heating system must be of equal importance We have to select the correct heating system for a particular application We need to have an adequate control system Building operatives should understand how to use a heating s stem correctl other ise it is use a heating system correctly, otherwise it is useless
Image of page 4
11/24/2009 5 Environmental parameters that influence thermal comfort: Air Temperature Mean Radiant Temperature Relative Humidity Air Velocity These parameters influence heat transfer by convection, radiation, and evaporation.
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
11/24/2009 6 Convective Heat Transfer Influenced by air temperature and air velocity Takes place continually It is imperceptible in most buildings because of low air speeds (below 0.1 m/s) To be perceptible, speeds must exceed 0.2 m/s
Image of page 6
11/24/2009 7 Radiant Heat Transfer I fl d b di t t t (t ) f Influenced by mean radiant temperature (t r ) of the surfaces within rooms Occurs between the skin/clothes and surfaces seen by the human body For cuboid shaped rooms, t r (at center of room): n n r t a t a t a t a t + + + + = ... 3 3 2 2 1 1 n a a a a + + + + ... 3 2 1 t r : mean radiant temperature ( C) a 1 , a 2 , … : room component surface areas (m 2 ) t 1 , t 2 , … : room component surface temperatures (m 2 )
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
11/24/2009 8 Evaporative Heat Loss Influenced by relative humidity of air and air velocity Evaporative heat losses are low in humid areas since the precipitation produced is hard to evaporate in such environments Evaporative cooling important at air temperature above 25 C Above 29 C, almost all heat losses by evaporation
Image of page 8
11/24/2009 9 Dry Resultant (Operative) Temperature t res : dry resultant temperature ( C) v a : air velocity (m/s) t : air temperature ( C) t a : air temperature ( t r : mean radiant temperature ( C)
Image of page 9

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon