power knot llc. report of efficiency gain at the hilton ... · by reacting to the temperature of...

Power Knot LLC. Report of Efficiency Gain at the Hilton

Hotel, Newark, California. 2011-07-21

Power Knot LLC

Report on the Installation of the RFE of 14

501 Valley Way

Milpitas CA 95035

Efficiency Gain at Hilton Hotel, Newark CA

Report on the Installation of the RFE

USA

+1-408-889-8433

www.powerknot.com

1 Summary

Power Knot installed the Refrigerated Food Emulator (RFE) in a walk in cooler in the kitchen at the Hilton Hotel in Newark, California. After installation, the energy consumed by the refrigeration system was reduced by over 16%, resulting in a savings in electricity and a reduction of carbon footprint.

The installation of the RFE ensures that the temperature of the food is more consistent resulting in greater quality and less spoilage.

The refrigeration system turns on less than 60% after installation of the RFE, resulting in less maintenance of the refrigeration system.

Figure 1. Hilton Hotel, Newark, California

http://www.powerknot.com/



2 Introduction

2.1 About the Hilton Hotel

The most recognized name in the industry, Hilton Hotels stands as the stylish, forward thinking global leader of hospitality. Today Hilton welcomes guests in more countries than any other full-service hotel brand, with more than 530 hotels and resorts in 76 countries across six continents. Hilton Hotels is part of the Hilton Worldwide group that operates nearly 3,750 hotels in 84 countries.

For more information about Hilton Hotels access:

http://www.hilton.com

Christopher Nassetta, President and Chief Executive Offi- cer of Hilton Worldwide stated, “Hilton Worldwide brands touch hundreds of communities and millions of people every day. That’s why operating in a responsible and sus- tainable manner is both a priority for our company and a central part of how we do business. Through our focus on sustainability, we intend to mitigate our impact on the environment, create economic value for our owners, and provide a better experience for our guests.”

2.2 The Problem

Hilton Worldwide has committed to a reduction of energy consumption between 2009 and 2014 from direct opera- tions of 20%.1

To meet these targets, Hilton is very interested in proven technologies that will help it meet this goal. The hotel real- izes that much energy is used on air conditioning and refrigeration and would like to save 15~25% of that energy.

2.3 The Solution

The Refrigerated Food Emulator (RFE) from Power Knot reduces the energy used by coolers or freezers to store food and saves customers money. The RFE is installed inside the cooler or freezer and causes the room thermostat to react to the temperature of the food and not the temperature of the air.

Figure 2. Equipment on rooftop at Hilton Hotel

1. Hilton Worldwide web site, retrieved 2011-07-11.

http://www.hilton.com/

http://www.hiltonworldwide.com/aboutus/commitmentaction.htm



By reacting to the temperature of the food in the cooler or freezer, the refrigeration system operates more efficiently and maintains the food at a more consistent temperature thereby reducing food spoilage.

Power Knot guarantees a minimum of 10% reduction of energy after the installation of the RFE. In the case of Hilton Hotel, this can translate to savings of cash, reduced maintenance, and reduction of carbon footprint.

The hotel chose to prove the efficacy of the RFE on a walk in cooler that is always in use in the kitchen. The cooler is shown in figure 17 on page 14.

3 About the Cooling Equipment

The system is a split air to air system with the compressor unit on the roof shown in figure 2.1 The compressor unit is one of many in a combined assembly with louvres on each side that provide adequate air- flow and easy access to the system. The size of the unit is approximately 2 tons (6.5 kW cooling capacity).

4 Test Procedure

4.1 Theory

To measure the gains in efficiency, Power Knot measured the performance of the system prior to and after the installation of the RFE. We take care in the process to ensure that accurate results are obtained. We will be able to calcu- late the increase in efficiency by taking the power (in Watt) before treatment, WB , and the power after treatment, WA :

gain in efficiency = WB – WA ---------------- WB

(EQ 1)

However, the performance of an air cooled air conditioning system is dependent on the outside air temperature (OAT). It is this air that cools the condenser; as the temperature rises, the temperature of the condenser rises. This causes greater pressure in the system and that in turn results in greater power usage. Thus, when the ambient conditions are changing, it is not possible to compare the power readings on one day with those on another day and draw a conclusion about power saved.

Figure 3. Showing the position of the OAT sensor

1. A split system is one in which the compressor and condenser are typically housed in one case while the expansion valve and evaporator are housed in another case, usually in the space to be cooled.



Therefore, we monitored the OAT with a sensor placed at the louvre where the air to cool the condenser is drawn from. This is shown in figure 3.

Inside the refrigerator, we measured the temperature and humidity of the air in the room. The air temperature rises as external heat warms the space. It also rises as people enter the space or as warm food is placed in the space for storage. The average temperature will reflect the temperature of the food in the cooler. This sensor is shown in figure 6.

4.2 Performance Monitoring

We measured the following parameters:

• power consumption of the system • outside air temperature (OAT) • air temperature and humidity inside the walk in cooler

We used a single logger to measure and store the power and OAT and we used a stand alone logger in the room to measure the temperature and humidity in the cooler. The equipment we used to make the measurements is listed in figure 5.

4.3 Logger Resolution

The Hobo data loggers make measurements every two seconds. They then average these measurements and save the data every one minute. Therefore, the resolution of any measured value is one minute and a value that changes faster than every two minutes may be averaged. However, the value that is recorded is accurate. The appearance of the value being incorrect is considered acceptable for this test as neither the temperature nor the power of the system should change that often.

4.4 Placement of the Loggers

Figure 4. Showing the position of the power measurement devices

We placed the data logger that reads the air temperature and humidity in the room as shown in figure 6. We tied the unit in place with a plastic tie wrap to ensure it did not move during the course of the test. The cable for the OAT sensor was fed through the equipment tray and then tied to the grille where the air is drawn to cool the condenser. Again, it was fixed firmly in place so that it would not move during the evaluation. This is shown in figure 3. The sensor was positioned where it never receives direct sunlight nor can it get wet when it rains. Therefore, these environmental conditions will not affect the reading.



Quantity Devices Manufacturer Part number Serial Number

1 Hobo data logger Onset Computer Corporation

H21-002 9680192, version 3.0.0

1 12-bit smart temperature sensor

Onset Computer Corporation

S-TMB-M017 9720458 (OAT)

1 Pulse input adapter (to connect WattNode to data logger)


S-UCC-M001 9664076

1 WattNode kWh trans- ducer, 240 Vac (pulse output)

Continental Con- trol Systems

T-WNB-3D-240 042984

2 Current transformer 20 A 333 mV output

Magnelab T-MAG-SCT-20 —

1 Temperature and relative humidity data logger


U10-003 9705690, version 1.0.0 (inside cooler)

Figure 5. Items used to measure power consumption, temperature, and relative humidity

To measure the power, we placed the current clamps inside the breaker panel and wired these to the Watt- Node as shown in figure 4. The current clamps were placed around the main power wires serving the a/c system. Therefore, we measured the total power consumed by the system, not just the power of the compressor. This power includes the fans used to circulate the air over the condenser and evaporator. The volt- age connections for the WattNode are made directly in the same panel. We placed the data logger on the base of the equipment tray. None of these connections was disturbed during the course of the test.

Figure 6. Reading the data loggers with a PC: (Left) in the cooler. (Right) on the rooftop



4.5 Reading the Loggers

We used a laptop PC to read the Hobo data loggers as shown in figure 6. The H21 logger is connected to the PC with a converter from serial to USB while the U10 logger connects directly with a USB cable.

We started to log the power and temperatures on Friday 2011-06-17 and finished logging on Thursday 2011-07-14. None of the equipment used to make any measurements was moved during this time.

5 Installing the RFE

Power Knot installed the RFE at 09:30 on Tuesday 2011-06-28. We needed to replace the thermostat as the existing one had a coil and not a gas bulb. The RFE fits over the gas bulb, so it was not possible to install the RFE with the existing thermostat. The installed RFE and new thermostat is shown in figure 7.

Figure 7. Showing the position of the new thermostat and the RFE



The thermostat that we used to replace the old thermostat was the same make and family as the old one. This meant it would have identical electrical and mechanical characteristics. We decided to replace the thermostat at the same time as the installation of the RFE so that we could compare the power used before installation against the power used after installation.

We needed to adjust the thermostat the next day as the setting on the new thermostat was too high. We subsequently verified the temperature of the food with and IR thermometer as shown in figure 8.

6 Results

6.1 Summary

Figure 8. Reading the temperature of the food with an IR thermometer

Figure 9 shows a tabular summary and figure 12 shows graphical summary of the data collected. For each day, there are 1440 measurements for temperature and power. These figures show the readings averaged over a full day. Figure 9 also shows the total number of times the compressor turned on during the day. Each day starts at midnight and ends at 23:59. All times are in GMT–7h because California was on day- light savings (summer) time during the evaluation.1

6.2 Temperature inside the Cooler

The average daily temperature inside the cooler increased slightly from an average of 40.2°C (4.5°C) to 40.5°C (4.7°C). This is as a result of replacing the thermostat. However, this is within limits for long term storage of food and the minor difference will have negligible impact on the results of the evaluation.

The logger inside the cooler could store results only for 18 days. It then stopped recording. Therefore, we have no temperature readings inside the cooler for the days of 2011-07-06 and 2011-07-07 shown in figure 9. We reset the data logger and continued to monitor after that date.

6.3 Ten Day Comparison

We monitored the system for ten days prior to installation of the RFE. The OAT (outside ambient temperature) varied widely during the test. As the temperature increases this has the effect of increasing the work that the compressor must do to expel the heat from the condenser. To compare the performance of the refrigeration system after installation of the RFE we need to select 10 days where the average daily temperature matches the ten days before the installation. These are:

1. The data collected on the first and last days are for partial days and are not shown in these figures.



Day Date

OAT

Power

Inside Temp

Compressor on times

Saturday 2011-06-18 Sunday 2011-06-19 Monday 2011-06-20 Tuesday 2011-06-21 Wednesday 2011-06-22 Thursday 2011-06-23 Friday 2011-06-24 Saturday 2011-06-25 Sunday 2011-06-26 Monday 2011-06-27

72.4°F 78.1°F 87.1°F 88.9°F 74.1°F 69.5°F 69.4°F 68.1°F 71.6°F 65.9°F

0.67 kW 0.89 kW 0.72 kW 0.63 kW 0.56 kW 0.49 kW 0.56 kW 0.55 kW 0.56 kW 0.50 kW

40.2°F 39.9°F 40.2°F 40.6°F 40.2°F 40.0°F 40.0°F 39.7°F 39.7°F 39.7°F

25 28 25 30 40 34 40 27 28 30

Tuesday 2011-06-28 Wednesday 2011-06-29

68.5°F 66.0°F

0.31 kW 0.40 kW

42.7°F 43.2°F

Installed RFE at 09:30 Adjusted temperature at 11:30

Thursday 2011-06-30 Friday 2011-07-01 Saturday 2011-07-02 Sunday 2011-07-03 Monday 2011-07-04 Tuesday 2011-07-05 Wednesday 2011-07-06 Thursday 2011-07-07 Friday 2011-07-08 Saturday 2011-07-09 Sunday 2011-07-10 Monday 2011-07-11 Tuesday 2011-07-12 Wednesday 2011-07-13

72.0°F 80.5°F 78.5°F 81.4°F 78.9°F 84.9°F 81.4°F 76.6°F 77.3°F 69.2°F 71.1°F 65.2°F 69.0°F 68.8°F

0.51 kW 0.59 kW 0.57 kW 0.67 kW 0.51 kW 0.51 kW 0.57 kW 0.50 kW 0.62 kW 0.55 kW 0.53 kW 0.46 kW 0.48 kW 0.47 kW

40.6°F 40.7°F 40.9°F 41.1°F 40.8°F 40.8°F

40.7°F 40.7°F 40.0°F 40.4°F 40.5°F 40.4°F

18 18 19 18 17 17 19 17 19 19 19 17 18 18

Figure 9. Tabular summary of results showing daily averages

• Saturday 2011-06-18 to Monday 2011-06-27. Average OAT = 74.5°F (23.6°C) • Monday 2011-07-04 to Wednesday 2011-07-13. Average OAT = 74.2°F (23.4°C)

The average OAT during these two periods can be considered the same and we can hence make direct comparisons about the power. The data for these two periods of ten days are shown in figure 10.

Date period

OAT

Power

Internal temperature

Compressor on times

Saturday 2011-06-18 to Monday 2011-06-27 74.5°F (23.6°C)

0.614 kW 40.0°F (4.5°C)

30.7

Monday 2011-07-04 to Wednesday 2011-07-13 74.2°F (26.5°C)

0.520 kW 40.5°F (4.7°C)

18.0

Differences –0.3°F (0.1°C)

15.4% 0.5°F (0.3°C)

41%

Figure 10. Performance comparisons for ten days before and ten days after installation of the RFE



Performing analysis as described in equation 1 on page 3 we have:

= WB – WA

= -----------------------------------

= 15.4% gain in power efficiency ---------------- 0.614 – 0.520

(EQ 2)

WB 0.614 6.4 Weekly Comparison

We can average seven days before installation with seven days after installation. The analysis of a week is better than a 10 day average because traffic in and out of the cooler at the weekend may be different from during the week so the weekly average is an accurate analysis. The two sets of seven days where the average temperature is similar are:

• Saturday 2011-06-18 to Friday 2011-06-27. Average OAT = 77.07°F (25.0°C) • Thursday 2011-07-04 to Wednesday 2011-07-10. Average OAT = 77.05°F (25.0°C)

The data for these two weeks are shown in figure 11.

Performing analysis as described in equation 1 on page 3 we have:

= WB – WA

= -----------------------------------

= 16.3% gain in power efficiency ---------------- 0.647 – 0.541

(EQ 3)

WB 0.647

Date period

OAT

Power

Internal temperature

Compressor on times

Saturday 2011-06-18 to Friday 2011-06-24 77.1°F (25.0°C)

0.647 kW 40.2°F (4.5°C)

31.7

Monday 2011-07-04 to Sunday 2011-07-10 77.1°F (25.0°C)

0.541 kW 40.6°F (4.8°C)

18.1

Differences 0.0°F (0.0°C)

16.3% 0.4°F (0.2°C)

43%

Figure 11. Performance comparisons for a week before and after installation of the RFE 6.5 Compressor Starts

Figure 9 shows the number of times each day that the compressor starts (and stops). We can see that the number of times the compressor starts each day after installation of the RFE is much fewer than before. This will reduce wear on the compressor and electrical system.

The weekly averages are shown in figure 11. The number of times the compressor starts has been reduced from an average of 31.7 per day to 18.1 per day, a reduction of 43%.



Figure 12. Graphical summary of results showing daily averages

6.6 Daily Comparisons

Referring to figure 9, we see three pairs of days when the OAT is similar before and after treatment. These are shown in figure 13.

Before RFE

After RFE

OAT before

OAT after

Delta OAT

Power reduction

I 2011-06-18 2011-06-30 72.4°F (22.4°C) 72.0°F (22.2°C) –0.4°F (–0.2°C) 24%

II 2011-06-19 2011-07-02 78.1°F (25.6°C) 78.5°F (25.8°C) +0.4°F (+0.2°C) 37%

III 2011-06-24 2011-07-12 69.4°F (20.8°C) 69.0°F (20.5°C) –0.4°F (+0.5°C) 15%

Averages –0.4°F (–0.2°C) 25%

Figure 13. Comparison of daily average power reductions

The power consumption and OAT for these days are shown in figure 14, figure 15, and figure 16.



Figure 14. Daily comparison (I). Before installation of RFE (2011-06-18) top and after (2011-06-30) bottom



Figure 15. Daily comparison (II). Before installation of RFE (2011-06-19) top and after (2011-07-02) bottom



Figure 16. Daily comparison (III). Before installation of RFE (2011-06-24) top and after (2011-07-12) bottom



+ +

Performing analysis as described in equation 1 on page 3, we have:

= WB – WA =

-----------------------------

= 24% gain in power efficiency, I ---------------- 0.67 – 0.51

(EQ 4)

WB

= WB – WA =

0.67

-----------------------------

= 37%

gain in power efficiency, II ---------------- 0.89 – 0.57 (EQ 5)

WB

= WB – WA =

0.89

-----------------------------

= 15%

gain in power efficiency, III ---------------- 0.56 – 0.48 (EQ 6)

WB 0.56

Averaging the results of equation 4, equation 5, and equation 6 we have:

average gain in efficiency = 24% 37% 15% ---------------------------------------- 3

= 25% (EQ 7)

7 Credits

Power Knot would like to thank the management and staff of the Hilton Hotel, Newark for their purchase order placed with Power Knot, for their invaluable assistance with the test, and for their patience while we visited frequently to take measurements and pho- tographs.

8 Conclusion

This study has drawn a conclusion for the energy savings over a week period of over 16% and over three sets of days of about 25%. We therefore conclude that the average savings are in excess of 16%.

Compressor starts were reduced by over 40% resulting in greater reliability of this equipment.

Figure 17. Entrance to walk in cooler in main kitchen



This is an example of the benefits of the Refrigerated Food Emulator (RFE) supplied and supported by Power Knot. For more information on the RFE, please contact your local sales representative or send an e-mail to Power Knot at [email protected].

Power Knot provides safe and economically sound solutions for businesses seeking to reduce energy costs and their carbon footprint through maximizing the efficiency of their cooling systems. Power Knot works with commercial, industrial, and military customers globally to reduce cooling system energy usage, improve energy efficiency, provide colder air, reduce maintenance expenses, and increase the lifetime of the systems. Their technologies are proven and available today, have been in reliable use for many years, and offer a payback period typically of less than two years. For more information, access www.powerknot.com.

Copyright © 2011, Power Knot LLC. All rights reserved. 2011-07-21.

mailto:[email protected]

http://www.powerknot.com/

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