Bill Chalmers- Gulf Coast Green 2010

Gulf Coast Green 2010 – Bill Chalmers P.E.

Gulf Coast GreenEnthalpy Wheel Fundamentals

Renovating the FutureApril 16, 2010


Energy Recovery Wheel Application Fundamentals

Bill Chalmers P.E., LEED® AP, CEM, GBP, CDTAgenda• How energy recovery wheels work •Why energy recovery wheels should be used• Rules to follow to avoid commonly made mistakes• Follow the rules to make jobs work well avoid giving energy recovery a bad reputation



• Ventilation is required for occupant health and comfort• Exhaust air required for toilets, odorous areas and general exhaust• Energy recovery uses the exhaust air to heat and cool outdoor air



How it Works – Sensible Heat Recovery• Wheel slowly rotates from one airstream to another• Wheel substrate (typically aluminum) transfers the heat•Transfer heat from hot outdoor air to relatively cool exhaust air in summer• Transfer heat from relatively warm exhaust air to cold outdoor air

Handout Page 7



How it Works – Latent Heat Recovery• Wheel slowly rotates from one airstream to another• Desiccant coating the wheel transfers moisture (latent energy)•Transfer moisture from humid outdoor air to dry exhaust air in summer• Transfer moisture from exhaust air to dry outdoor air • Vapor pressure differential is the driving force transferring water vapor.

Handout Page 6


Water vapor in supply air stream is adsorbed on the desiccant

Because the vapor pressure in the colder exhaust air stream is lower the water vapor pressure on the desiccant surface, the water is desorbed and exhausted back to the outside

Molecular sieve is a man made material with controlled pore openings to adsorb only certain type of vapors and gases.

Pore opening

Supply Air

Outdoor Air

Return Air


Latent heat (moisture) transfer Handout


Outdoor Air97°F, 64 gr/lb

(69.1°Fwb)

Supply Air80°F, 63.2 gr/lb

Return Air75°F, 64 gr/lb(50% R.H.)

Exhaust Air92°F, 63.8 gr/lb

Effectiveness =(97-80)/(97-75) = 77.3%

Cooling Mode (Peak Design Day) Lubbock, TX


Handout Page 9


Outdoor Air11°F, 5.4 gr/lb

Supply Air60.4°F, 49.9 gr/lb

Return Air75°F, 64 gr/lb(50% R.H.)

Exhaust Air25.6°F, 18.5 gr/lb

Effectiveness =(75-11)/(60.4-11) = 77.2%


Heating Mode (Peak Design Day) Lubbock, TX

Handout Page 9



1100 Peachtree, Atlanta GAOperates 5 days/week, 12 hours/day

Conventional ERU

Outdoor air 52,000 cfm

Exhaust air 31,200 cfm

Capital cost – AHU

$56,000 $110,000

Capital cost – Chiller

$91,000(260 tons)

$43,000(123 tons)

Capital cost – Electric preheat

$7,000(600 kW)

$0

Total Capital Cost

$182,000 $176,000

Annual Savings $51,100



Rule #1 – Energy Recovery is worthwhile even if exhaust air is 50% of outdoor air and occupied hours are limited• Take capital cost credit for chillers, heating, humidifiers and electrical service.• Typically, energy recovery is free.

Conventional ERU




$56,000 $110,000


$91,000(260 tons)

$43,000(123 tons)


$7,000(600 kW)

$0

Total Capital Cost

$182,000 $176,000

Annual Savings $51,100



Rule #2 – Do not size chillers, boilers, heating coils and electrical service for cooling and heating loads if the wheel fails.• If wheel fails, fix it. • Use whatever cooling and heating is available and decrease the outdoor air quantity during failure.• If building has multiple units and operation is critical, allow extra capacity for one wheel failure.

Conventional ERU




$56,000 $110,000


$91,000(260 tons)

$43,000(123 tons)


$7,000(600 kW)

$0

Total Capital Cost

$182,000 $176,000

Annual Savings

$51,100



Rule #3 Collect all available exhaust air• restrooms• janitors closets• general lab exhaust• general exhaust• locker rooms• copy rooms Do not include kitchen, laundry or fume hoods.The greater the amount of exhaust air, the higher the wheel efficiency.



Rule #4 Decide the acceptable type of wheel • 8” deep aluminum substrate• 2” deep mylar substrateIf mylar is acceptable, then specify it because it is almost certainly less expensive than aluminum.



Rule #5 Select the allowable wheel velocity• I recommend 700 to 800 fpm and maximum 1” w.g. APD.• Manufacturers recommend 500 fpm. Manufacturers also like selling bigger wheels.

Size 43 Size 28

Velocity (fpm)

500 750

APD (in. w.g.)

.45 .72

Efficiency .87 .83

Handout Page 8



Preface to Rules #6, 7,8 and 9• Cross contamination must be minimized by:

• fan configuration •seals• purge• desiccant type

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Silica Gel (No humidity transfer)

Silica Gel (With humidity transfer)

4A Molecular Sieve (No humidity transfer)

4A Molecular Sieve (With humidty transfer)

3A Molecular Sieve (With humidity transfer)



Rule # 6 Select Fan Configuration• Exhaust air must be negative relative to outdoor air to prevent cross contamination• I recommend configuration 1 because return air is usually slightly negative relative to outdoor air path.• Blow through supply fan is usually very positive relative to return air causing high purge volumes and noise. I recommend avoiding this configuration.

Handout



Rule # 7• Allow for purge volume in fan selections

Handout Page 15



Rule #8 Choose between labyrinth seals and brush seals

Handout Page 5



Rule #9Choose desiccant type• 3 Angstrom cross contaminates the least. Use for critical applications such as general lab exhaust and hospitals

3

PORE DIAMETER DISTRIBUTION VARIOUS DESICCANTS

A B C

D

E

A) Molecular sieve 3A D) Activated alumina B) Molecular sieve 5A E) Silica gel C) Molecular sieve 13X

Pore Diameter (angstroms)

Kinetic Diameters of Various Molecules (angstroms)

Material Dia. (A)

Helium Hydrogen Water Nitrix Oxide Carbon Dioxide Sulphur Dioxide Carbon Monoxide Methane Ethane Propane Propylene Difluochloromethane(R22) Sulphur Hexafloride Benzene Carbon Tetrachloride

2.6 2.9 2.7 3.2 3.3 3.6 3.8 3.8 3.9 4.3 4.5 4.9 5.5 5.9 5.9

5 10 25 50 100

• 4 Angstrom recommended for most applications. • I recommend against other desiccants, particularly if odorous exhaust like from restrooms and janitor’s closet is being exhausted



Rule #10• ALWAYS put minimum MERV 6 filters upstream of wheel on supply AND exhaust • Wheels can be cleaned, but large items (bugs, trash) can clog and damage the wheel.



Rule #11• In cold climates, put the preheat coil upstream of the wheel on the supply air to avoid frosting and freeze stat tripping.

Handout Page 20



Rule #12Control sequence:• If outdoor air enthalpy is above the exhaust enthalpy, run the wheel at 100%• If outdoor air enthalpy is below the exhaust enthalpy, but outdoor air temperature is above supply air temperature, wheel is off• If outdoor air temperature is below supply air temperature, modulate the wheel to achieve the supply air temperature.Handout Page 19 to 21



Rule #13• Install air pressure measurement across supply and exhaust to measure airflows.

Return Air Supply Air

Exhaust Air

Outside Air

®

Outside Air Damper

Exhaust Air Damper



Rule #14• Use two control valves sized for 1/3 and 2/3 flow respectively to allow for low flow conditions.• This is particularly important if the coil is selected for wheel failure.



Rule #15• Never say energy recovery does not fit!• Select the wheel at 700 fpm and use high velocity in the outdoor air and exhaust section.

Plan View

Section View



Rule #16• wheel manufacturers are good at making wheels• air handling manufacturers are good at making air handlers• controls companies are good at doing controlsSpecify an air handler complete with wheel installation and include a control sequence for the controls vendor.

Plan View



Rule #17 – Obey Rules #1 to #16When energy recovery goes bad, it gives the technology a bad reputation and all the benefits are lost

Torn plenum wall Fan fell off its

base



Thanks for your interest!I am available until 2 pm if more information is needed.

Bill Chalmers- Gulf Coast Green 2010

Design

Transcript of Bill Chalmers- Gulf Coast Green 2010