humidity control and heating and cooling applications · optimizing solutions through superior...

Optimizing Solutions through Superior Dehumidification Technology SM

Humidity Control and Heating

and Cooling Applications December 6, 2018

Today’s Discussion

• Discussion of cooling, heating and

dehumidification loads.

• Importance of zone condition selection on

efficiency.

• Airflow energy impact through HVAC

equipment and room.

• Basic equipment options and energy use.

• Critical importance of commissioning.

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ROOM LOADS

Lights and Water

(and others)

Relative Intensity of Lighting

Relative Intensity of Lighting at

Specific Wavelengths

Relative Intensity of Lighting at

Specific Wavelengths

Lighting Summary

• Even with 45-65 watts / sq. ft. the PAR value is less than full noon summer sun.

• Although plants use a small amount of the light energy in the process of converting water into sugars, starches, and O2, virtually all lighting energy becomes sensible heat load.

• Total input (including ballasts or drivers) is important.

Evapotranspiration

• Latent loads.

• Evaporation highly dependant on irrigation method.

– Drip Irrigation – Low evaporation.

– Flood or Trough Irrigation – Higher rate.

– Spray Irrigation – Extremely high evaporation.

• As much as 300 Btu/hr for large plant in high light.

• Perhaps best estimated by (water in) – (water out); if

known.

Evaporation + Plant Transpiration

Plant Physiology – Water Transport

Transpiration

Evaporative Cooling Effect

• As water evaporates energy is converted.

1060 Btu/lb at typical conditions.

• Plants also use this effect in the transpiration

process to cool themselves. Through

conduction and convection this in turn cools

the air.

• Care must be observed if used to offset

loads. If plants are just emerging, water use

and evaporative cooling effect are small.

Facilities Construction

• Can vary significantly.

• Room within room.

• Structurally insulated panels (or similar).

• Partitioned room.

• Open warehouse.

Typical Rooms

Load Details

Building Skin Loss/Gain – If Applicable

• Insulated (or uninsulated) walls, floors, and

ceilings.

• Heat loss as ambient temperature decreases.

• Heat gain as ambient temperature increases.

• Concrete floors create a heating load.

• Doors and windows have different losses and

gains than the walls.

• Solar load has major impact if it exists.

Ventilation for Plants

• Outdoor air exchange may be required to

maintain CO2 levels for plants.

• Adds (or subtracts) sensible and latent

load.

• Alternative in a “Closed (Sealed) Growing

Environment” is CO2 supplementation.

– Rooms may be kept at higher temperature.

Relative Humidity

…is relative…

It represents the ratio of moisture in the air

relative to when no more can be held in

the air. (Saturated)

…but..

Relative Humidity

Relative humidity is relative to temperature!

Higher temperature air is able to hold more

moisture. Lower temperature hold lesser

amounts before saturation.

Therefore, RH changes with temperature!

Changes in Dry Bulb Temperature Affect Relative Humidity

Changes in Dew Point

Affect Relative Humidity

Relative Humidity is

Relative

Higher Enthalpy(More Energy Rich)

Lower Enthalpy (Lower Total Energy)

Lines of Constant Enthalpy

Transpiration Rates – Lights On

• Leaf temperature determines the vapor

pressure in the leaf.

• Air temperature and humidity determines

the vapor pressure in the air.

• Vapor Pressure Deficit (VPD) drives

transpiration – regulated rates are

important for plant growth and health.

Transpiration Rates – Lights Off

• Stomata closed as no light is being

received. Evapotranspiration continues at

a lower rate during lights off.

• Slowly decreases over 60-90 minutes.

Roughly 30% of full light moisture rate

when full dark.

• This latent load can still be relatively high

as sensible load is negligible.

VPD at 1.3 kPa (0.39” Hg) at various DB/WB/RH

Different operation, but same drive for growth

Larger Equipment/Higher Energy Use

Smaller Equipment/Lower Energy Use

Calculation Methods for Latent Load

Net Watering Rate given or calculations

Derivations of Penman-Monteith equation or similar

Total Loads and Control - HIDDesign Conditions –3,500 ft2, 2,000 plants,

63 watts/sq ft. (85% BE), 318 gal/day net water – Early Veg

500 CFM Ventilation - Lights On

Description Sensible (Btu/hr) Latent (Btu/hr)

Lighting and Appliance 852,500 0

Doors 445 0

Ceiling 5,331 0

Walls 4,564 0

Infiltration -320 -199

Ventilation -6,510 -7,770

Evapotranspiration 0 150,404

Evaporative Cooling Effect -150,404 -

Total 705,606 142,435

Compiled using ACCA Manual N Form N1 and ASHRAE Dehumidification Weather Data

705,606/(142,435 + 705,606) = 0.83 SHR

Total Loads and Control - LEDDesign Conditions –3,500 ft2, 2,000 plants,

25 watts/sq ft. (95% DE), 318 gal/day net water – Early Veg

500 CFM Ventilation - Lights On

Description Sensible (Btu/hr) Latent (Btu/hr)

Lighting and Appliance 314,078 0

Doors 445 0

Ceiling 5,331 0

Walls 4,564 0

Infiltration -320 -199

Ventilation -6,510 -7,770

Evapotranspiration 0 150,404

Evaporative Cooling Effect -150,404 -

Total 167,184 142,435

Compiled using ACCA Manual N Form N1 and ASHRAE Dehumidification Weather Data

167,184/(142,435 + 167,184) = 0.54 SHR

Total Loads and Control - HIDDesign Conditions –3,500 ft2, 2,000 plants,

63 watts/sq ft. (85% BE),954 gal/day net water–Early Flower

500 CFM Ventilation - Lights On

Description Sensible (Btu/hr) Latent (Btu/hr)

Lighting and Appliance 852,500 0

Doors 445 0

Ceiling 5,331 0

Walls 4,564 0

Infiltration -320 -199

Ventilation -6,510 -7,770

Evapotranspiration 0 526,414

Evaporative Cooling Effect -526,414 -

Total 326,596 518,445

Compiled using ACCA Manual N Form N1 and ASHRAE Dehumidification Weather Data

326,596/(326,596 + 518,445) = 0.32 SHR

Total Loads and ControlDesign Conditions – 3,500 ft2, 2,000 plants,

954 gal/day net water - Flower

500 CFM Ventilation - Lights Off

Description Sensible (Btu/hr) Latent (Btu/hr)

Lighting and Appliance 1,203 0

Doors 445 0

Ceiling 5,331 0

Walls 4,564 0

Infiltration -320 -199

Ventilation -6,510 -7,770

Evapotranspiration 0 175,471

Evaporative Cooling Effect -175,471 -

Total -170,758 167,502

No cooling required. Dehumidification Only Load.Compiled using ACCA Manual N Form N1 and ASHRAE Dehumidification Weather Data

Lights On

Lights Off

Air conditioner and dehumidifier

Lighting Load

Air conditioner and dehumidifier

Lighting Load

Reheating

Energy use and control

• Traditional dehumidifiers heat the air when it may not be needed.

– Cooling needs to work “harder.”

• Some equipment has less than full capacity reheat or electric reheat only.

– “New” energy needs to be added.

– Not considered here.

• “All-in-one” environmental control is best practice.

Multiple Units Serving a Space

Multiple Units Serving a Space

• Partial capacity during

maintenance/service.

• Redundancy possible.

• Footprint and layout advantages.

• Enhanced staging capability.

– Energy efficiency.

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Control coordination is critical

Economizers

• Number of hours where OA is possible is variable depending on the location and time of year.

• More care required for filtering with air economizer. May introduce more spores and pests.

• Both the temperature and humidity are affected if economizer is used. This must be approached carefully.

• CO2 Enhanced grows impractical with OA economizer.

Outdoor Air Too Warm in Lights On

Outdoor Air Too WarmFew Hours in Lights Off

Outdoor Air too Humid

Will require more energy to heat or humidify.

May not be able to properly cool or dehumidify

Target76° Dry Bulb

45% RH

IMPACTS OF AIRFLOW

Affinity Laws Working for Energy Efficiency

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Affinity Laws (Fan Laws)

Affinity Laws (Fan Laws)

Affinity Laws (Fan Laws)

For example, reduction in the airflow (shaft speed) to ½ of the peak flow rate in a given system results in

1/8 of the peak power at the fan shaft.

Importance of Air MovementPlant Leaf Boundary Layer

• Water vapor builds at leaf boundary layer.

• Creates higher relative humidity and vapor pressure at leaf

surface.

• Buildup can happen under canopy.

– Dicots have most stomata on underside of leaf.

– 20-30% higher relative humidity under canopy if airflow is too

low.

Slowly moving canopy is goal

Δ 7.8 Btu/lb

10-tons Capacity (120,000 Btu)3400 CFM

Δ 17 grains/lb

Moisture Removed = (3400 CFM *17 grains per lb) / 1555 = 37.2 lbs Water Removed

Δ 22°F

Sensible Cooling= (3400 CFM *Δ 22°F TD) * 1.08 = 80,784 Btu/h

Δ 15.6 Btu/lb

10-tons Capacity (120,000 Btu)1700 CFM

Δ 44 grains/lb

Moisture Removed = (1700 CFM *44 grains per lb) / 1555 = 48.1 lbs

Δ 34°F

Sensible Cooling= (1700 CFM *Δ 34°F TD) * 1.08 = 62,424 Btu/h

COMMISSIONING

Critical Steps in Ensuring Success

Commissioning

• Startup by factory trained technicians who know the equipment.

• Equipment and facility in operation.

– Challenge with this application.

– A project manager with timeline is key.

• Have operators/facility people available during startup for Owner Training.

• Have local Service Technicians aligned for PM and ready in case of any issues.

Continuous Commissioning

• Periodic Maintenance for this type of

equipment is key.

• Complete a “Start-up” on a yearly basis.

• Review trends to determine if there is an

issue.

• “An ounce of prevention is worth a pound

of cure.”

Sensor Locations and

Central Control

79°/55%

72°/65%

76°/50%

85°/35%

60°/11% 76°/55%

Controls Tuning

Tune Changes

Remote Monitoring

• Remote monitoring.

– E-mail and SMS alerts.

– Cloud-based service.

– Real-time data and logging.

– Allows a team to review together quickly.

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Thank you!

Craig Burg

Desert Aire, LLC

craig@desert-aire.com