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Field Test of a DHW Distribution System: 

Temperature and Flow Analyses

C. Dennis Barley, 

Bob Hendron, and 

Lee Magnusson

2010 ACEEE Hot Water 

Forum

Ontario, California

May 13, 2010

NREL/PR-550-48385
Innovation for Our Energy Future

Scope of This Presentation

Field test of a DHW distribution system in an occupied 

townhome 

(Previous presentation by Lee Magnusson et al., ACEEE 2008)

Additional data, further analysis:

Measured fixture flows and temperatures

(Some surprising results)

Tested recirculation system 

(Surprising result)

Evaluated disaggregation of flow by:

• Measured Temperatures

• Aquacraft Trace Wizard analysis

• Comparison.
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Description of Home

Solar Row, in Boulder, Colorado

3-story, 1,700 finished ft2

+ Semi-finished basement, 587 ft2

3 bedrooms, 2 occupants.

Solar DHW/space combination system

Condensing boiler backup

Unit 1→

Credit: Paul Norton/NREL
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Description of Data Acquisition System

Flow meters: 

• Each fixture hot

• Total DHW and total water

• (Cold water flow = total water – total DHW)

Thermocouples:

• Hot at each fixture

• Master shower pipe

• Cold at kitchen sink (enables mixed water temperature calculation)

Campbell CR1000 datalogger with TC and pulse 

multiplexers

5-second records during flow events
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Flow Results: All Fixtures

* Note: 

The measured total daily hot water flow is only 41% of the Building America Benchmark 

value of 54.7 gal/day for a 2-bedroom (2-person) home.

Avg % Avg SDV Avg SDV Avg SDV

Master bath shower 10.4 46.4 372 158 6.21 2.80 0.98 0.14

Kitchen sink 5.0 22.2 30.9 33.7 0.33 0.54 0.46 0.31

Dishwasher 3.0 13.2 65.2 42.5 0.96 0.71 0.78 0.17

Master bath sink 1.8 8.0 28.2 32.5 0.35 0.61 0.50 0.31

Washing machine 1.8 7.9 49.9 34.1 0.96 0.69 1.10 0.29

2nd bath sink 0.3 1.4

1st floor bath sink 0.1 0.5

2nd bath shower 0.1 0.5

TOTALS: 22.5* 100.0

Fixture Daily Volume, Gal Event Duration, s Event Volume, Gal Flow Rate, Gal/m
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Flow Results: Dishwasher

Ratio of hot-to-total water 

flow rate,

before Thot=105 F.

Average value = 1.03.

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0.10.20.30.40.50.60.70.80.91.01.11.21.3

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• Ratio should be =1 consistently.

• Note size of measurement errors 

(single cold water measurement).

• Note simultaneous usage.

Ratio of hot-to-total water 

flow rate,

after Thot=105 F.

Average value = 0.97.
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Flow Results: Washing Machine

Ratio of hot-to-total water 

flow rate,

before Thot=105 F.

Average value = 0.53.

Ratio of hot-to-total water 

flow rate,

after Thot=105 F.

Average value = 0.95.

Washing machine control strategy:

• Hot & cold for 40 sec, then hot only.

• Results in Tmix ≈ 92 F (not 76 F)
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Flow Results: Master Bath Shower

Ratio of hot-to-total water 

flow rate,

before Thot = 105 F.

Average value = 0.69.

Ratio of hot-to-total water 

flow rate,

after Thot = 105 F.

Average value = 0.87.

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• Was cold water run in the shower 

while waiting for warm-up?

• Was cold water run elsewhere?

• Single cold water measurement is 

ambiguous.
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Temperature Results: Shower

Mixed water temperature* at master bath shower. 

Average = 110.4 F. SDV = 4.6 F.

(* Median of 5-second samples after Thot = 105 F)

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8084889296

100104108112116120124128132

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Temperature Results: Sink

Mixed water temperature* at kitchen sink.

Average = 109.7 F. SDV = 10.6 F.

(* Median of 5-second samples after Thot = 105 F)

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Recirculation System: Description

Purpose: To try to measure runoff of water during 

warm up at the fixtures, by comparing periods with 

recirculation off and on.

Configuration: Three zones.

Control: Occupant detectors turn pump on.

Temperature sensor on return pipe turns pump off.

Sensitivity set high to avoid false negatives.
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Recirculation System: Effect on Flow

Without recirculation: 3591 255 gal

With recirculation: 3099 328 gal

Difference (14%): 492 416 gal

(90% confidence interval)

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Apr-07 Nov-07 Jun-08 Dec-08 Jul-09 Jan-10

Hot Water Flow, gal

Cold Water Temperature, 0F

Off On
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Recirculation System: Effect on Energy

Without recirculation: 222 82 kWh (44% of load)

With recirculation: 709 101 kWh (165% of load)

Difference : 487 131 kWh

(90% confidence interval)

(Note: DHW volume was 3,590 gal when off, 3,060 gal when on.)

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Apr-07 Nov-07 Jun-08 Dec-08 Jul-09 Jan-10

Cold Water Temperature, 

Auxiliary DHW Energy, kWh

0F

Off On
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Recirculation System: Effect on Energy
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Flow Disaggregation Methods: About

Temperature Disaggregation

• Temperatures measured in hot water pipes at the fixtures

• Identify which fixture drew hot water based on temperature rise

• Method described by:

Weihl, J.S. and Kempton, W. (1985). “Residential Hot Water Energy Analysis: 

Instruments and Algorithms.” Energy and Buildings, Vol. 8, pp. 197-204.

Aquacraft Trace Wizard© Software

• Given sample data from various fixture flows

• Given aggregate hot water usage data

• Identify which fixture drew hot water based on the draw pattern.
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Flow Disaggregation Methods: Results

% error is based on comparison to fixture flow meter data (“truth”).

A: Temperature disaggregation is for single flows only; % error by event.

B: Trace Wizard disaggregation includes multiple flows; % error by volume.

TemperatureA TraceWizardB

Sinks 14.1% 17.1%

Shower 2.4% 11.1%

Dishwasher Not measured 6.5%

Clothes Washer 12.1% 7.2%

Percent Error in Fixture ID
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Conclusions

1. In this home, mixed water temperatures average 110 F, 

unlike the common assumption of 105 F.

2. To measure cold water flow, fixture flow meters are 

recommended.

3. Our test protocol for the effects of recirculation didn’t 

work very well, because of extraneous variables (noise).

4. Flow disaggregation by temperature:

• Accuracy is comparable to Trace Wizard analysis

• More apparatus is required (thermocouples)

• Useful temperature data are also collected.
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(Error Analysis)

y = -0.0077x + 3.1413

y = -0.0411x + 5.013

y = -4.7243x + 343.98

y = -3.3243x + 347.85

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Auxiliary DHW Energy, kWh

Fluid Flow, klit

Groundwater Temperature, °F

Flow, No-Circ

Flow, Recirc

Energy, No-Circ

Energy, Recirc

Linear (Flow, No-Circ)

Linear (Flow, Recirc)

Linear (Energy, No-Circ)

Linear (Energy, Recirc)