Mark Cherniack Howard Reichmuth New Buildings Institute

RTU Savings Research Project

RTU Savings Research Project: Findings and Recommendations

Regional Technical ForumFebruary 3, 2009

Mark Cherniack

Howard Reichmuth

New Buildings Institute



• Phased RTU Research program– Phase 1: Identify the known savings and cost-

effectiveness data; establish priorities for Phase 2 research

– Phase 2: Conduct the Phase 1 recommended research activities

– Phase 3: To be determined by outcome of Phase 2; an expanded field test was envisioned


Phase 2 RTU Research Project

• Bench test controller/sensor issue

• Apply field measurement and service protocol to RTUs

• Develop an annual savings methodology based on the measured data

• Review existing utility RTU program data

• Propose a Phase 3 work plan


Review Existing Data Set

• 70% had the controller being tested

• 1% used enthalpy sensors with unknown drift and calibration, although only dry-bulb sensing is necessary in our climate

• 56% had only a single stage of cooling wired, which significantly curtailed economizer use

• 73% used single changeover point (one outdoor sensor and no return air sensor), 27% used a differential changeover strategy


Phase 2 RTU Research ProjectBench Test

• Economizer control problem identified

• Tested specific Honeywell controller/sensor combo

• Found 6-10 degF deadband in sensor-limited economizer cooling

• Honeywell verifies sensor finding

• Recommendations made for new sensor


RTU Savings Research ProjectBench Test

5

Models Overview

2 degree dead band10 degree dead band

-40 to 149F (-40 to 65 C)shipping temp

-40F to +150F (-40to 66C)shipping temp

-40 to 149F (-40 to 65 C)ambient temp

35F to +100F (+4C to +38C)ambient temp The deviceremains operational afterexposure to extremes of Š40to 125F (-40C to 52C)

8 Selectable changeovertemperatures

Dry bulb changeover based onA, B C and D setting oneconomizer module

Underwriters Laboratories Inc.Flammability Rating: UL94-5V

Underwriters Laboratories Inc.Flammability Rating: UL94-5V

2 models2 models

C7660C7650


RTU Savings Research ProjectBench Test- Honeywell Sensor Specs

Analog circuit based on C7400 circuit

Microprocessor based control with +/- 1 degree F hysteresis

10 to 20 mA output signal to economizer logic module

4 OR 20 mA output signal to economizer control; At 4 mA not OK to economize, 20 mA OK to economize

C7650 C7660


RTU Savings Research ProjectBench Test Recommendations

• Ensure that the old Honeywell sensor is not being used in new HVAC units coming in through utility HVAC EE programs

• Notify a wide band of HVAC market stakeholders

• Establish benefits of adding the new sensor to utility RTU field service protocols

• Consider regional bulk sensor purchase


RTU Savings Research Project RTU Field Measurement & Service Protocol

• 9 initial sites recruited; 5 have little cooling load. 3 sites provided sufficient signature data for analysis and consideration

• Metering was more than sufficient for the minimum monitoring package

• Analyzed three preliminary Bonneville sites


RTU Savings Research ProjectRTU Service Protocol

• Thermostat reset and/or replacement

• Measured airflow through the evaporator

• Economizer system check

• Additional control potential

• Refrigerant charge check/adjustment as needed


RTU Savings Research ProjectRTU Monitoring

• RTU total power

• RTU fan power

• Gas burner status

• Damper position

• Condensate flow

• Outdoor air temperature (2 measurements)

• Return/mixed (4 measurements) temperatures

• Supply air temperature


RTU Savings Research ProjectRTU Monitoring Results

RTU Electric Energy Performance Map - BI1 Unit 1

0

20

40

60

80

100

10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00

Mean 24 Hour Temperature, deg F

RT

U E

lec

tric

En

erg

y, k

Wh

/da

y

RTU Electric Signature


RTU Savings Research Project Anatomy of an RTU Energy Signature

• Cooling balance point temperature

• ‘Flat’ low temperature slope

• Cooling slope



RTU Gas Signature

RTU Gas Energy Performance Map - BI1 Unit 1

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

10.00 20.00 30.00 40.00 50.00 60.00 70.00

Mean 24 hr temperature, deg F

Ga

s E

ne

rgy

Us

e, B

urn

er

hrs

/da

y

Burner hrs/day Predominant Mode Low Efficiency Mode



% Outside Air Map

Temperatures by mode

-20

-15

-10

-5

0

5

-30 -20 -10 0 10 20 30

Oat-Rat

Mat

-Rat stage1

stage2

circ



Economizer Control Map - BI unit #2

45

50

55

60

65

70

75

80

60 62 64 66 68 70 72 74 76

Return Air Temp, deg F

Ou

tsid

e A

ir T

em

p, d

eg

F

on

off

Economizer Control Temperature Map


RTU Savings Research ProjectBonneville Unit

hourly max kw vs temp

0

2

4

6

8

10

12

0 10 20 30 40 50 60 70 80 90 100

Hour average outside temp

Ma

x k

W

max kw

Hourly Max Power vs Temperature



RTU Electric Energy Performance Map - BI unit 2

0

20

40

60

80

100

120

40 45 50 55 60 65 70 75 80


RT

U E

ne

rgy

, k

Wh

/da

y

econo

no econo

Economizer Effect


RTU Savings Research ProjectAnnual Savings Methodology

• Average daily site temperature

• Daily RTU energy [electric/gas] signature

• Histogram of site daily normal avg temperature

@ 5 degF bins (consistent with Bonneville data)

• Signature x histogram = daily RTU energy

• Normalized annualized RTU energy is annual

sum of daily RTU energy


RTU Savings Research ProjectAnnual Savings Methodology

#1 Finding: With a few weeks pre- and

post-data on a regularly operating

building, an estimate of annual energy

use and therefore savings, can be

reliably made. Data needs to be studied

in detail to gain confidence in

interpreting the results.


RTU Savings Research ProjectKeys To Annual Savings Methodology

• 4 diagnostic graphs are needed for a high

confidence energy savings estimate

– Mode by power map = accurate kW savings

– % outside air map

– Economizer temperature control map

– RTU energy performance map


Preliminary Bonneville Site RTU DataSite 895

RTU performance Map

0

10

20

30

40

50

60

70

80

90

100

30 35 40 45 50 55 60 65 70 75

Mean 24 hr temp, deg F

To

tal

en

erg

y,

kW

h/d

ay

Initial RTU Performance Map



Comparison Day RTU Energy

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time Hour of Day

RT

U E

ner

gy,

kW

h/h

r

pre

post

Daily RTU Energy Profile



RTU Performance Map with Models

0

20

40

60

80

100

120

30 35 40 45 50 55 60 65 70 75


RT

U E

ne

rgy

, k

Wh

/da

y

kWh

pre

post

RTU Performance Map


Preliminary Bonneville Site RTU Data Site 895 - 8900 kWh savings

RTU Annual Energy by Temperature Bins

RTU Annual Energy

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70 70-75 75-80 80-85

Daily Average Temperature Bin

Ann

ual R

TU E

nerg

y, k

Eh

no econo

econo



RTU Performance Map


0

10

20

30

40

50

60

70

80

90

100

30 35 40 45 50 55 60 65 70 75


RT

U E

ne

rgy

, k

Wh

/da

y

kWh

pre

post

post




RTU Annual Energy

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70 70-75 75-80 80-85

Average Daily Temperature Bin

An

nu

al R

TU

En

erg

y

post

pre




0

10

20

30

40

50

60

70

30 35 40 45 50 55 60 65 70 75


RT

U E

ne

rgy

, k

Wh

/da

y

kWh

pre

post

post

RTU Performance Map




R T U An n u al En erg y

0

500

1,000

1,500

2,000

2,500

15-20 20-25 25-30 30-35 35-40 40-45 45-50 50-55 55-60 60-65 65-70 70-75 75-80 80-85

Av e r a ge D a i ly T e m p e r a tu r e e B in

Ann

ual R

TU E

nerg

y

p o s t

p re


RTU Savings Research Project Recommendations - Phase 3

• Apply measurement/monitoring protocol--

>> To all remaining Bonneville existing sites

>> In all new field monitoring projects including the Premium Ventilation Package and Bonneville’s upcoming field monitoring project [60+ sites?]

• Current models should be reconciled to existing/new unit level data

• Subset monitored annually at least 5 years

• Fan power savings are very important: 24-hr operation

• More aggressive economizer control: pre-cooling

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