Rooftop PackageHVAC

Operations and Maintenance Measures:David Baylon

Stan PriceBob Davis

Rooftop Fundamentals

• Packaged air handler with heating and cooling source built in– Typically gas fired heating with compressor cooling– Economizer required by all regional codes for

equipment above 5 cooling tons (less in some cases)– Building ventilation handled by the package unit with

outdoor air introduced into the mixed air plenum• Almost 80% of all HVAC systems use this sort of

package technology• Particularly important in small commercial and

“big box” applications in suburban and exurban applications

Operational Issues

• Most economizers are assumed to provide up to half of the cooling requirement

• Surveys of economizer operation concluded that at least 50% are broken or not optimized

• Simple controllers, inaccurate sensors, and primitive dampers insure minimal functionality in many units.

• O&M contracts seldom extend to unit operation or efficiency

PSE Premium Rooftop Service

• Operated since 2003 with about 10 contractors

• Serviced about 2000 rooftop units

• Provided training for about 150 service technicians

• Focused on economizer and air flow

• Limited to units under 25 tons

Analysis Packages

• Package 1: Basic Service– Check thermostat type/settings– Measure economizer airflows; adjust as needed– Adjust economizer changeover temperature– Clean coils

• Package 2: Basic Service/Repair– Basic Service plus– Wire/enable morning warm-up control (heating savings)– Repair outside air or return air damper

• Package 3: Thermostat– Basic Service plus– Install two-stage cooling thermostat– Wire/enable morning warm-up control

Analysis Package (Cont.)

• Package 4: CO2 Control– Basic Service plus– Add CO2 sensor and needed economizer controller

• Package 5: Conventional controller– Basic Service plus– Replace economizer controller

• Package 6: Controller plus thermostat– Basic Service plus– Install 2 stage cooling thermostat and new econo. controller

• Package 7: New Economizer– Install new economizer on existing unit and – Perform Basic Service

Cost of Measures

Cost Assumptions:

Basic Service 350

Thermostat 200

Controller 250

CO2/Controller 600

Warm-up Relay 100

Economizer 1500

• Assumes a 5-10 ton rooftop unit

• Annual maintenance normalized to a 5 year basic maintenance cycle

• Applied to 7.5 ton, 3000 sf zone

Assumptions

• Cooling equipment modeled at 8.3 EER• Heating equipment efficiency .80• 3000 square feet, 7.5 ton RTU (single zone operation

and control)• 20% Make-up air setting (Package 1,3,5,7)• 30% Make-up air setting (Package 4,6)• 50% Make-up air (Stuck damper, Package 2)• 35% mixed air leakage (65% maximum outside air)• LPD: 1.55 w/sf, office. 3.05 w/sf, retail• Broken damper: stuck at 50% make-up• No warm-up control• 55 F economizer change-over

Seattle Office

Pac

kage

Base Treatment Savings Cost Life O&M

Heating Cooling Heating Cooling Heating Cooling

kWh/sf kWh/sf kWh/sf kWh/sf kWh/sf kWh/sf $/sf yrs $/sf

Basic 5.01 1.43 5.01 0.95 0.00 0.48 0.12 15.00 0.02

Repair 9.56 1.14 4.65 0.95 4.92 0.19 0.15 15.00 0.02

T-Stat 5.01 1.43 4.65 0.95 0.37 0.48 0.22 15.00 0.02

DCV 6.46 1.37 2.13 0.95 4.34 0.42 0.32 15.00 0.02

Control 5.01 1.43 4.65 0.95 0.37 0.48 0.20 15.00 0.02

Reset 6.46 1.38 4.65 0.95 1.82 0.43 0.27 15.00 0.02

New Econ 5.01 1.61 4.65 0.98 0.37 0.63 0.62 15.00 0.02

Rooftop O&M Boise Office

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2.00

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14.00

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kW

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Heat

Heat Save

Cool

Cool Save

Boise, Office

Pac

kage

Base Treatment Savings Cost Life O&M

Heating Cooling Heating Cooling Heating Cooling

kWh/sf kWh/sf kWh/sf kWh/sf kWh/sf kWh/sf $/sf yrs $/sf

Basic 6.79 2.32 6.79 1.90 0.00 0.42 0.12 15.00 0.02

Repair 12.99 2.31 6.43 1.90 6.57 0.42 0.15 15.00 0.02

T-Stat 6.79 2.32 6.43 1.90 0.37 0.42 0.22 15.00 0.02

DCV 8.82 2.34 2.92 1.80 5.90 0.54 0.32 15.00 0.02

Control 6.79 2.32 6.43 1.90 0.37 0.42 0.20 15.00 0.02

Reset 8.82 2.38 6.43 1.90 2.40 0.48 0.27 15.00 0.02

New Econ 6.79 2.38 6.43 1.85 0.37 0.53 0.62 15.00 0.02

Rooftop O&M Seattle Retail

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Heat Save

Cool

Cool Save

Seattle Retail

Pac

kage

Base Treatment Savings Cost Life O&M

Heating Cooling Heating Cooling Heating Cooling

kWh/sf kWh/sf kWh/sf kWh/sf kWh/sf kWh/sf $/sf yrs $/sf

Basic 1.83 3.69 1.83 2.50 0.00 1.19 0.12 15.00 0.02

Repair 6.32 3.08 1.76 2.50 4.56 0.58 0.15 15.00 0.02

T-Stat 1.83 3.69 1.76 2.50 0.07 1.19 0.22 15.00 0.02

DCV 3.56 3.73 0.72 2.41 2.84 1.32 0.32 15.00 0.02

Control 1.83 3.92 1.76 2.50 0.07 1.42 0.20 15.00 0.02

Reset 3.56 3.73 1.76 2.50 1.80 1.23 0.27 15.00 0.02

New Econ 1.83 4.30 1.76 2.53 0.07 1.77 0.62 15.00 0.02

Rooftop O&M Boise Retail

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kW

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Heat

Heat Save

Cool

Cool Save

Boise Retail

Pac

kage

Base Treatment Savings Cost Life O&M

Heating Cooling Heating Cooling Heating Cooling

kWh/sf kWh/sf kWh/sf kWh/sf kWh/sf kWh/sf $/sf yrs $/sf

Basic 2.38 4.64 2.38 3.79 0.00 0.85 0.12 15.00 0.02

Repair 7.17 4.50 2.31 3.79 4.86 0.71 0.15 15.00 0.02

T-Stat 2.38 4.64 2.31 3.79 0.07 0.85 0.22 15.00 0.02

DCV 4.26 4.99 1.24 3.66 3.02 1.33 0.32 15.00 0.02

Control 2.38 5.09 2.31 3.79 0.07 1.30 0.20 15.00 0.02

Reset 4.26 4.99 2.31 3.79 1.95 1.20 0.27 15.00 0.02

New Econ 2.38 5.29 2.31 3.78 0.07 1.51 0.62 15.00 0.02

Results

• Overall savings in Seattle are about 1300 kWh for cooling and about 40 Therms heating without repairs

• Repairs or CO2 control increases heating savings by a factor of ten.

• Costs for Basic Service packages vary from $350 to $800 (higher cost includes thermostat and controller)

• Costs for CO2 sensor plus needed controller with Basic Service is about $950