Calculating Energy Savings

Q. I want to calculate the energy savings associated with reducing washer bath temperature. J.W.

 

A. This question was posted to the Cleaning and Pretreatment Forum on PF ONLINE. That is a very good and timely question. I think more people today are looking for ways to decrease their energy costs than in the past and this trend will likely continue. The typical finishing operation will have many tanks to heat and also ovens. Since no further information was available from JWs question, I will list the following assumptions I used so we could see what kind of savings we were talking about. I assumed:

• 1 heated tank containing (essentially) water.
• The tank contains about 1,000 gal of liquid.
• Tank dimensions are 5 × 5 × 5.5 ft deep.
• Initial water temperature and part temperatures to be cleaned are 60°F.
• The shop runs this tank on two shifts per day, five days per week, 50 weeks per year and shuts it down every day on the off shift.
• The tank processes 500 pounds per load, and four loads per hour.
• Although it varies significantly, I estimated natural gas at $10/1,000 cu ft.
• I did the estimate assuming the current operating temperature is 160°F and the proposed temperature is 120°F. (see Table below)

 

Description	Current (160°F)		Proposed (120°F)
Heat Up	50 times per year at 837,500 Btu each time		50 times per year at 502,500 Btu each time
Surface Losses(ventilated)	The losses from the ventilated tank surface will be 40,000 Btu/hr or about 160,000,000 Btu/yr		The losses from the ventilated tank surface will be 14,000 Btu/hr or about 56,000,000 Btu/yr
Tank Losses	23,750 Btu/hr (uninsulated) 95,000,000 Btu/yr	5,625 Btu/hr (insulated) 22,500,000 Btu/yr	11,250 Btu/hr (uninsulated) 45,000,000 Btu/yr	3,750 Btu/hr (insulated) 15,000,000 Btu/yr
Loading Losses	20,000 Btu/hr, 80,000,000 Btu/yr		12,000 Btu/hr, 48,000,000 Btu/yr
Totals (annual)	376,875,000 Btu/yr (uninsulated)	304,375,000 Btu/yr (insulated)	134,125,000 Btu/yr (uninsulated)	144,125,000 Btu/yr (insulated)
Cost ($/yr)	$3,725	$3,000	$1,720	$1,425

 

Following this, you need to consider several steps related to heat up and operating losses.

The chart is for only one tank and assumes lowering the operating temperature from 160°F to 120°F.

This would indicate that a reduction in the range of about 50% is possible in cost savings. Another obvious benefit is insulating your tanks. A shop could derive a significant benefit from both an energy and safety standpoint. The amount of savings here is significant and should be multiplied by the numerous tanks that are present in a typical finishing shop including rinses and other finishing/plating baths. The above calculation is for an immersion tank. A spray wash system would be expected to loose even more energy due to the higher evaporative cooling when spraying a fluid. Those savings would be even more significant and are not included here.