project

Abstract

A facility is planning a major expansion and will need to modify its chiller plant configuration in order to compensate for larger cooling needs. The chiller plant with two electric-centrifugal chillers has already offered by the facility. The design group has to satisfy the new cooling load after the expansion by evaluating possible plant configurations. Four alternative solutions are presented with their respective tabulated thermal calculations. The alternatives are defined as a base case. The alternatives are: a full storage 4-hour ice TES system, a full storage 12-hour ice TES system, and a partial storage ice TES system respectively. These four systems are analyzed by the design group to find both operating and capital costs. The payback period for all the alternatives are able to be calculated once the operating and capital costs are determined by analyzing in order to find out the best solution. The results were achieved after analyzing and the results will be presented below in the section called “Result and Discussion”.

Introduction

The unit of cooling load is given as tons, final values have to be converted to kWh using the equation presented below:

(1)

Where,

The conversion 3.517 is used to convert tons to kW,

Assuming a

Once the electricity consumption is determined, the operating costs can be calculated based on the Time-of-Use (TOU) electric rates listed below:

· on-peak (1:00 pm – 5:00 pm): $0.5/kWh

· mid-peak (10:00am – 1:00 pm, and 5:00 pm - 10:00 pm): $0.3/kWh

· off-peak (10:00 pm - 10:00 am): $0.1/kWh

Depending on the time when the chillers are running, the operating costs are calculated using the following equation:

The capital costs of each system can be determined depending on each system’s cooling output in tons. The list below shows the price per ton (PPT) for the different systems:

· Electric centrifugal chiller plant cost: $2400/ton

· Ice-making chiller cost: $900/ton

· Ice TES cost: $500/ton-hour

The capital cost can be determined by using the presented equation below

Result and Discussion

Base Case: No thermal energy storage

The first case is used a base case that do not have thermal energy storage, which purchase one additional 1,300-ton chiller. By calculating with cooling load and TOU electricity rate, the calculating is able to get Centrifugal Chiller Electricity Consumption and Operating cost.

Table1: Thermal Calculation for base case

The Chiller electricity consumes 49,202.83 kWh per day with a cost of $13,997. Also, the capital cost is $3,120,000.

Equation of Capital cost:

Alternative1: Full storage 4-hours ice TES system

This case is alternative 1 considering a full storage. The machine about external ice TES works over 20 hours except on-peak hours of each day. The central ice TES system includes the two existing 1,300ton electric centrifugal chillers, and a new 7,000-ton-hour ice TES system. Also, it consists of two underground ice storage tanks, a 350ton ice making chiller. The machine related to alternative1 works during the 4hour of the on-peak electric.

Table2: Thermal Calculation for Alternative1

In the table2, the Centrifugal Chiller electricity uses to 40,996.5kWh per day, and the operating cost is determined $11,371.164 per day. The operating cost by alternative1 is $9152.5 per day, which can save $2218.64 per day. The capital cost consists with a 350-ton ice making chiller and a 7,000-ton-hour ice TES system. The capital cost is $3,815,000.

The payback period for alternative1 with an operating cost and a capital cost determines 4.71 years.

Alternative2: Full storage 120hours ice TES system

This case is alternative 2 analysing a full storage ice TES system. The machine related to alternative2 works during the 12 mid-peak and off- peak hours (from 10:00pm to 11:00 am). The general system is similar to that of Alternative 1, but the ice-making chiller is estimated at 584 tons.

Table3: Thermal Calculation for Alternative3

In the table3, the Centrifugal Chiller electricity uses to 40,996.5kWh per day, and the operating cost is determined $10,714.658 per day. The operating cost by Alternative 2 is $8,347.128 per day, which can save $2,367.53 per day. The capital cost is determined $4,025,600.

The payback period for alternative2 with an operating cost and a capital cost determines 4.66 years.

Alternative3: Partial storage (load levering strategy) ice TES system

This case is alternative3 analysing a partial storage ice TES system. The machine related to Alternative3 works during all hours of the day. The general system is similar to that of Alternatives 1 and 2, but the ice-making chiller is estimated at 292 tons. Also, the ice storage requires to be reduced to 5,836 ton-hours.

Table4: Thermal Calculation for Alternative3

In the table4, the electricity uses to 40,996.5kWh per day, and the operating cost is determined $11,807.272 per day. The operating cost by alternative3 is $10,137.102 per day, which can save $1670.17 per day. The capital cost is $3,180,800

The payback period for alternative3 with an operating cost and a capital cost determines 6.17 years.

Alternative 4 – Design Group Alternative and Economic Analysis:

Alternative 4 was a created by the group to try to achieve a shorter payback period. This alternative is similar to alternative 2, except it uses an 875-ton ice-making chiller for 8 hours during the off-peak hours instead of 12. The rest of the system is the same as alternative 2, meaning it uses the existing centrifugal chillers and has a 7000-ton ice TES system. Table 5 below shows the results achieved for the energy usage and operational costs per day highlighted.

Table5: Thermal Calculation for Alternative 4

The electricity usage was determined to be 49202.83 kWh per day and the daily operating costs are $10,714.66. The capital cost is shown below:

With an operating cost of $10,714.66 per day and a capital cost of $4,287,500 the payback period is determined to be about 5.88 years.

Comparison

Summary