Energy Efficient Heating Ventilating and Air Conditioning

Facility Energy Balance

Fundamental Equation

Qf = [(A/R + V pcp) (Tia – Toa) – Qint] / Eff

• A = area of envelope• R = thermal resistance of envelope• V = air flow rate• pcp = product of air density and specific heat• Tia = inside air temperature• Toa = outside air temperature• Qint = internal heat gain• Eff = efficiency of heating equipment

Energy Saving Opportunities

Increase insulation: R Decrease outdoor air flow rate: V Decrease inside air temperature: Tia Maximize utilization of internal heat: Qint Increase efficiency: Eff

Increase Insulation

Insulate Un-insulated Walls/Ceilings

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

0 2 4 6 8 10 12 14 16 18 20

Initial R-Value

Savi

ngs

(Btu

/ft2-

yr)

Diminishing return of increasing insulationAdding R=10 hr-ft2-F/Btu and (Tia – Toa) = 35 F

Insulate Metal Walls

Insulate walls with spray-on cellulose or closed-cell foam

Cover Single-pane Glass with Double-Wall Polycarbonate Sheets

Replace Single Pane Skylights with Double-Wall Polycarbonate

R = 1 to R = 4Heating Cost Saving = $0.90 / ft2-yr

Cost = $2 / ft2

Insulate Dock Doors

Reduce Air Flow

Air Flow Fundamentals

MAU

VMAU = 50 cfm

VEXAUST = 100 cfm

VLEAK = 50 cfm

• Air flow in = Air flow out• Most plants exhaust more air than MAUs supply• Causes negative pressure and infiltration• Infiltration air reduces comfort, and heating energy

Close Doors and Openings

Install garage-door openers on lift-trucks to close shipping doors!

Close Doors and Openings

Install garage-door openers on lift-trucks

Observation: Heating energy varies by 3X at same temp!

Discovery: Didn’t close shipping doors!

Seal Unused Exhaust Fans

Reduce Stack-Driven Infiltration

Roof Louver

Annealing Furnace

Storage Yard

Plant

Unit Heater

Unit Heater

Closed Door

Stack Effect

240 ft

Roof Louver

Annealing Furnace

Storage Yard

Plant

Unit Heater

Unit Heater

Stack Effect

Turn Off Excess Exhaust/Ventilation

Turn Off Dust Collectors When Not In Use

Shut Blast Gates to Dust Collectors When Not In Use

Filter and Return Clean Air to Plant

Filter and Return Clean Air to Plant

Scrap Paper Collector

Install VFDs on Vent Hoods

Supply Outside Air to Exhaust Air Locations

Supply Outside Air to Exhaust Air Locations

Scrap Transport System

Reverse Exhaust Fan Direction to Utilize Heat from Equipment

Balance Plant Air Pressure with Differential Pressure Controlled MAUs

dP

VFD

Vmau = 100 cfm MAU

Vexhaust = 100 cfm

Vleak = 0 cfm

Manometer measures pressure difference and adjusts MAU air flow Good choice if ventilation requirements change frequently (paint

booths, etc.) Minimizes infiltration and facilitates lower inside air temperature

Use Indoor Heaters For Envelope Loss and Make-up Air Units to Heat Outside Air

Unit/IR/air rotation heaters– Reheat indoor air/space– 80% efficient since exhaust combustion gasses

Direct-fire make-up air units– Bring in and heat outside air– 100% efficient since combustion gasses added to

outside air Selection:

– Heating outside air, even at 100% efficiency, requires more energy than re-heating inside air at 80% efficiency.

– Use unit/IR heaters to make up envelope losses– Use make-up air units to heat outside air

Reduce Indoor Air Temperature

Move Thermostat Off Exterior Walls

Use Programmable Thermostats

• Lower/increase interior set-point temp during unoccupied periods

• Important because heating/cooling load proportional to (Tia – Toa)

• Example: If Toa = 50 F, then reducing Tia from 70 F to 60 F decreases heating load by 50%

• However, thermal mass limits temperature drop and reduces savings

50

55

60

65

70

75

0 5 10 15 20 25

Hour of Day

T (F

)

Tia (F) Tsetpoint (F)

Reduce Temperature Stratification With High-Volume Low-Velocity Fans

Problem– Excess

temperature stratification

Solution– Install

destratification fans

Reduce Temperature Stratification With Gas-Fired Infrared Heaters

Problem– Warm air removed by

exhaust fans or openings

– Excess temperature stratification (warm air near ceiling)

Solution– Install radiant heaters

Decrease Space Cooling Energy

Replace Dark Roof with White Roof

White roofs reflect sunlight and reduce roof cooling load by over 50%

Use Economizer For Year-round Cooling

Economizers vary positions of dampers to use outdoor air when Toa < Treturn

Qload

Qcooling coil

Return Air

Outdoor Air

Building Zone

Damper

Return Air Damper

Outside Air Damper

Identify Economizer Failure with LEA

Cooling slope should flatten at low temps Broken and missing damper gears

Verify Economizer Savings

In year-round cooling, can reduce cooling electricity use by ~40%

Increase Cooling Air Set-point Temperature During Cool Weather

Higher cooling air set-point temperature: Increases cooling load offset by economizer Decreases re-heat (if any) Decreases compressor load.

Qload

Qcooling coil

Return Air

Outdoor Air

Building Zone

Damper

Return Air Damper

Outside Air Damper

Purchase High-Efficiency Roof-top Units

Case Study 1

• Reduce winter ventilation & balance air pressure • Weather-adjusted gas use reduced by 51%.

Case Study: Reduce Winter Ventilation & Balance Air Pressure

Case Study: Reduce Winter Ventilation & Balance Air Pressure

• Reduce Winter Ventilation & Balance Air Pressure

• Weather-adjusted baseline gas use reduced

by 51%.