phase_Change_materials

USE OF RENEWABLE PHASE CHANGE MATERIALS

TO REDUCE CARBON DIOXIDE EMISSIONS

Galen J. Suppes, Michael J. Goff, and Shailesh Lopes,

Department of Chemical Engineering, W2028 Engineering Bldg. East,

Columbia, MO, 65211

Abstract

Phase change materials (PCM) can reduce heating, ventilation, and air conditioning (HVAC)

costs by a number of different mechanisms, including: eliminating air conditioning costs by

storing nighttime coolness for use during the day, eliminating heating costs by storing daytime

warmness for use during the night, and by load-shifting of electricity through thermal storage.

Well-designed strategies and utilization of phase change materials could easily reduce

HVAC-related carbon dioxide emissions by more than 25% from current levels. It is

anticipated that these reductions in emissions can be achieved while saving consumers money

and creating new markets for agricultural commodities. Greenhouse gas reduction potential of

PCSs is further enhanced by producing them from fats and oils. This paper summarizes

experimental data on the synthesis of PCMs from beef tallow and quantifies the cost and

greenhouse gas savings from their use.

Introduction

Figure 1 summarizes carbon dioxide emissions in the U.S. by sourcei[1]. As evident by Figure

1, electrical power generation is the largest producer of carbon dioxide emissions, and

furthermore, emissions in this sector are growing faster than any other sector. When

electricity is combined with residential and commercial fossil fuel heating, the sum of 33.9%,

5.4%, and 3.4% total a massive 42.7% of the total greenhouse gas emissions. Due to

magnitude of this contribution to greenhouse gas emissions, thermal energy storage can pave

the way to reducing carbon dioxide emissions to 1990 levels or less for decades to come. In

many if not most instances, reductions in greenhouse gas emissions can be achieved while

saving the consumer money.

Thermal energy storage can reduce greenhouse gas emissions through multiple mechanisms,

including: 1) Peak load shifting of electricity, 2) Eliminating part of the heating or air

conditioning loads, and 3) Enhance the performance of alternatives to fossil fuel combustion

heating. The purpose of this paper is to provide an introduction into the topic of phase change

materials and to describe how phase change materials can reduce greenhouse gas emissions

through each of the three indicated mechanisms.

Phase change material store coolness or warmness, typically through a latent heat of freezing

that is about one hundred fold greater than sensible heat. I is the most commonly used phase

change material and is used to keep food cool in a cooler or a drink cold in a cup.

While a 0C storage in ice can be used to store coolness for a house, it would require a more

expensive air conditioner and consume more energy to go to this low temperature as compared

to typical evaporator operation at about 10C. Alternatively, a phase change material that freezes at 15C freezes at a high enough temperature to be frozen by a conventional air

conditioner while freezing at a low enough temperature to provide a temperature driving force

to keep the house cool. Particularly good and efficient strategies can be developed to enhance

HVAC applications through the proper choice of phase change material with a freezing point

typically between 15C and 35C.

Figure 1. Summary of carbon dioxide emissions by source in the United States.

While some inexpensive salts have been demonstrated for HVAC applications, these salts have

two performance problems: 1) they are corrosive and 2) the hydrates typically used in the

15-35C temperature range are often not stable for prolonged storage and cycling in HVAC

applications.

Narrow freezing point range paraffin waxes distilled from petroleum are often the product of

choice. These waxes typically sell for prices greater than $0.35 per pound. When compared

to the price of fats and oils ranging in price from $0.10 to $0.30, derivatives of fats and oils can

be prepared at lower costs than paraffin waxes. These new fat and oil products are made from

renewable resources and have the potential to undercut the paraffin waxes on price. Fatty acid

derivatives of fats and oils are able to meet a range of energy storage means in the 15-35C

temperature range. Current research by the authors of this paper has a focus on low-cost and

high conversions of natural fat and oil products for PCM applications.

Efficiency for Energy Storage 0500100015002000250019881990199219941996199820002002YearMass of Carbon Dioxide (Tg)ElectricityTransportationIndustryAgricultureResidentialCommercial