Do Refrigerants have more heat capacity than water?

In summary, the report prepared by PNNL states that using refrigerant for heating and cooling requires less energy due to its larger heat capacity compared to air and water. This means that less mass flow is needed to achieve the same amount of heating or cooling. This is supported by the fact that the latent heat of vaporization for Chlorodifluoromethane (R22) is 233 kJ/kg, which is higher than the specific heat capacity of water. Additionally, other refrigerants can have a larger temperature range, including the boiling point, which allows for a higher heat capacity and lower mass flows.
  • #1
rollingstein
Gold Member
646
16
I was reading this report prepared by PNNL which says (page 16):

"Using refrigerant to deliver heating and cooling requires less energy because of the larger heat capacity of the refrigerant relative to air and even water. Less mass flow is needed to deliver the same amount of heating or cooling."

http://www.gsa.gov/portal/mediaId/169771/fileName/GPG_VRF_Report_-_FINAL_DRAFT_4-16-13

Is this really true? I see for Chlorodifluoromethane (R22) a latent heat of vaporization of 233 kJ/kg.

How is that more heat capacity than water?
 
Engineering news on Phys.org
  • #2
Latent heat of vaporization is not the same as heat capacity.
 
  • #3
Simon Bridge said:
Latent heat of vaporization is not the same as heat capacity.

What is the usable heat capacity of R22 in a typical refrigerant application? I assumed that was the latent heat.
 
  • #4
Is "useable heat capacity" a term of the art somewhere? Please provide a reference.
Check your assumptions against what the author is talking about - i.e. ability to transport heat compared with air and water.
Remember to compare like with like - what is the latent heat of vaporization for air? Does it make more sense, in that case, to compare the specific heat capacity (at constant pressure say)?
 
  • #5
Something important that you forget is the temperature range you can use when transporting heat from the room unit, which will be at room temperature and the chiller on the roof where the temperature must be above freezing if you use water. The temperature range will be less than 20 degrees K if you use water. Other refrigerants can have a much larger temperature range that can include the boiling point, so you have to include the heat of vaporization as well.
 
  • #6
willem2 said:
Something important that you forget is the temperature range you can use when transporting heat from the room unit, which will be at room temperature and the chiller on the roof where the temperature must be above freezing if you use water. The temperature range will be less than 20 degrees K if you use water. Other refrigerants can have a much larger temperature range that can include the boiling point, so you have to include the heat of vaporization as well.

Understood, thanks!

So essentially we are comparing H_vap_R22 versus Cp_H2O * delta_T_H2O

With a delta_T_H2O of 20 C the refrigerent gives a higher heat capacity i.e. lower mass flows.
 

1. Do refrigerants have a higher heat capacity than water?

Yes, refrigerants generally have a higher heat capacity than water. This means that they can absorb and store more heat energy per unit mass.

2. Why are refrigerants used in refrigeration and air conditioning systems?

Refrigerants are used in these systems because of their high heat capacity and their ability to absorb and release heat energy at low temperatures. This allows them to efficiently cool a space or object.

3. How does the heat capacity of refrigerants affect their use in refrigeration and air conditioning?

The high heat capacity of refrigerants is essential for their use in these systems. It allows them to effectively absorb heat from a space or object and release it outside, resulting in the cooling effect.

4. Do all refrigerants have the same heat capacity?

No, different refrigerants have different heat capacities. This is due to variations in their molecular structure and composition. Some refrigerants may have a higher heat capacity than others, making them more efficient for certain applications.

5. Can the heat capacity of refrigerants be changed?

The heat capacity of refrigerants is a physical property that is inherent to the substance and cannot be changed. However, engineers may choose to use different refrigerants with varying heat capacities based on the specific needs of a system or application.

Similar threads

Replies
1
Views
1K
  • Materials and Chemical Engineering
Replies
10
Views
2K
  • Introductory Physics Homework Help
Replies
4
Views
2K
  • Introductory Physics Homework Help
Replies
3
Views
1K
  • Introductory Physics Homework Help
Replies
3
Views
3K
  • Introductory Physics Homework Help
Replies
8
Views
5K
Replies
2
Views
1K
  • Classical Physics
Replies
2
Views
1K
Replies
6
Views
2K
Replies
3
Views
3K
Back
Top