Maximizing Payback

A contractor recently asked me what kind of paybacks we see with rainwater harvesting. Some suppliers say that there is NO payback, and from what I've seen of their product, I would agree! But I'm seeing paybacks as short as 5 years, which is pretty good on equipment with a 20 year WARRANTY. The elements that make for fast payback are:

1. Lots of nonpotable demand. Cooling tower makeup and irrigation are best candidates. How much is the landscaping worth, if there's another total watering ban? In Atlanta, we've had 2 summers in the past 20 years where outside watering was totally banned. Can we assume a 10% annual likelihood in the future?

2. Minimal piping. Locate the tank close to the piping. Stay out from behind walls. Until rainwater is generally approved as a potable water source, we will have to steer clear of using it for toilet flushing when retrofitting. Just too much labor installing a second set of piping.

3. High water costs. Atlanta's are the highest in the country, and are expected to continue to rise at 5-10% per year for the foreseeable future.

4. High impervious surface charges. Atlanta doesn't have these YET, but Gwinnett, Dekalb, East Point, and others do. 

5. High sewage costs. Some areas allow you to eliminate the sewage costs for cooling towers and irrigation, and some don't. Dekalb no longer offers separate irrigation meters. . . they need the money!

6. Use the right equipment. Above ground tanks are now $1-2/ gallon. Below ground tanks can run $4/gallon or more, depending on installation. How much granite is in the ground in Atlanta???

Yaskawa IQ Drives replace control panels. No treatment for cooling tower or irrigation. The submersible well pump in a sleeve design has been replaced with rainwater-specific submersible pumps. Piping to the tank can now go through the base, eliminating the need for heat tracing pipes. 

7. Does the owner value environmental responsibility? The above-ground tanks show customers and employees a conservation mindset. It might translate into more sales or motivated employees. 

Have you evaluated a project and found the payback period to be excessive? Send us the numbers, we love to value engineer.

~R

Rainwater Harvesting at High Schools

Saving the Earth and Saving Money

We have found a few combinations of water supply and demand that are the absolute top when it comes to payback. The common them is:

1. Ample supply of high quality water. Rooftops are best, especially rooftops made of metal or EPDM.
2. Significant demand of water that doesn't require much (or any) treatment.
3. Minimal piping changes.

Here's today's example, a typical high school in the Atlanta area.  On this one, we assumed that:

1. School is out June and July.
2. No cooling tower.
3. We would turn off the irrigation November – March.

The conclusions? 

1. To store enough rainwater to irrigate 100% with rainwater would require collecting all winter. Over 1,000,000 gallons storage required. Not cost effective.
2. Using available rainwater for irrigation will reduce total water consumption by approximately 50%, enough to qualify for maximum Potable Water Reduction LEED points.
3. Toilet flushing is not as cost effective as irrigation. The pumping, treatment, and plumbing are all more expensive.

And the data behind it:

	12 Hour Occupants		900	1 Hour Occupants - 900				0
	Occupancy Rate		100.00%	Building Size (s.f.)				220,000
	Roof Size		120,000	Occupied Hours				12
	Irrigation Area (s.f.)		200,000	GPD Toilets				2,700
	Average RainFall (in)	Average Cooling Load	Occupancy Days	Available	Cooling Tower	Irrigation	Toilet	Potential Rainwater Storage	Supplemental Water Needed
Jan	4.2	0.073	18	296,856	6,244		48,600	242,012	(242,012)
Feb	4.67	0.072	20	330,076	6,843		54,000	269,233	(269,233)
Mar	4.81	0.121	22	339,971	12,650		59,400	267,921	(267,921)
Apr	3.36	0.206	21	237,485	20,557	496,000	56,700	(335,772)	335,772
May	3.67	0.291	22	259,396	30,422	496,000	59,400	(326,427)	326,427
June	3.95	0.433	2	279,186	4,115	496,000	5,400	(226,329)	226,329
July	5.27	0.44	2	372,484	4,182	496,000	5,400	(133,098)	133,098
Aug	3.9	0.44	15	275,652	31,363	496,000	40,500	(292,211)	292,211
Sept	4.47	0.359	19	315,940	32,413	496,000	51,300	(263,774)	263,774
Oct	3.41	0.179	23	241,019	19,564	496,000	62,100	(336,645)	336,645
Nov	4.1	0.151	20	289,788	14,351		54,000	221,437	(221,437)
Dec	3.9	0.101	18	275,652	8,639		48,600	218,413	(218,413)
Total:	49.71		202	3,513,503	191,344	3,472,000	545,400	(695,241)	695,241