What are the Costs of Operating a No Recycle System vs. a Closed-Loop Water Recycling System?
Purpose:
To analyze some costs of operating an in-line aqueous cleaner that drains to a sewer (no recycle) compared to an aqueous cleaner with all of its water reused in a closed-loop water recycling system. Energy calculations are based on the use of an electric heater.Operating Assumptions:
Rinse flow (gpm) 4 | Water/sewage fees($/gal) $0.005 |
Operating hours(weekly) 30 | Cost of power($KWH) $0.050 |
Weeks/year 48 | Recycle system dumps(gal/yr) 10,000 |
Operating temerature(degrees F) 140 | Evaporation loss in cleaner(% total throughout) 4% |
Tap water Temperature(degrees F) 50 | Energy loss(estimated) 10% |
Heat Capacity 1 BTU/1B-degree F | Cleaner drain temperature(degrees F) 135 |
Note: Other values more specific to your application can be used for the above operating assumptions.
A. No-recycle water/heat costs
1. Water cost
Minutes/yr = 30hr/wk x 60 min/hr x 48 wk/yr = 86,400 minutes/yr
Gallons/yr = 86,400 min/yr x 4 gal/min = 245,600 gallons/yr
Water cost = 345,600 gallons/yr x $0.005 (water/sewage fees/gal) = $1,728.00/yr2. Heat cost
Heat required = 1 lbs tap water/yr x heat capacity x (oper. temp - tap temp)
Heat required = 345,600 gals/yr x 8.33 lbs/gal x 1 x (140 -50) = 259,096,320 BTU
Heat cost = 259,096,320 BTU/yr x 0.0002923 kwh/BTU x $0.05/KWH = $5,514.69/yrTotal water and heat costs = Water cost + heat cost = $1,728.00 + $3,786.69 = $5.514.69/yr
B. Recycle water/heat costs
1. Water cost
Gallons/yr - Dumps + Evaporation losses = gal water dumped/yr + (% loss x gal/yr for
no-recycle system) = 1000 gal/yr + 4% (345,600/yr) = 14,824 gal/yr.
Water cost = 14,824 gal/yr x $0.005 (water/sewage/fees/gal) = $74/yr.
2. Heat cost
Heat for tap water = tap water (lbs/yr) x heat capacity x (oper temp - tap temp) = 123,484 x 1 x (140 -50) = 11,113,560 BTU/yr
Heat required for recycled water:
Lbs recycled/yr = total rinse flow (lbs/yr) - evaporation losses = 345,600 gals/yr x 8.33
lbs/gal - 10%(2,878,848) = 2,590,963 lbs/yrHeat for recycled - lbs/yr recycled x heat capacity x (oper temp - drain temp) = 2,590,963 x 1 x (140 -135) = 12,954,815 BTU/yr
Total heat required = heat for tap water + heat for recycled water = 11,113,560 +
12,954,815 = 24,068,375 BTU/yrHeat cost = 24,068,375 BTU/yr x 0.0002923 KWH/BTU x $0.05/KWH = $352/yr
Total water and heat costs = Water cost + Heat cost = $74 + $352 = $426/yr
C. Summary
Recycled No-recycle Savings
Water/sewage $74 - $1,728 = $1,654
Heat $352 - $3,787 = $3,435Total $426 - $5,515 = $5,089