Long story short, the Amtrol "study" is like testing a speedboat in a bathtub. Then claiming the speedboat cannot do what the manufacturer says it will. What else would you expect from a company who only makes pressure tanks? We do not expect tank manufacturers to be happy about the superior performance of the Cycle Stop Valve over standard pressure tank systems.
The only thing this "study" got right was to highlight some of the problems with variable speed pumps. Short and intermittent uses of water were not a problem with the Cycle Stop Valve, as it did decrease the cycles and delivered more of a constant pressure than either the VFD or the tank only system. The numerous cycles per day documented with a variable speed pump would be devastating.
Amtrol's Test of Constant Pressure Systems,
Not Valid in Real World Applications
"Constant vs. Consistent Pressure" is a "study" by Amtrol, which Joe Lane published as an article in the August 2003 issue of WWJ. "Constant Pressure" systems are best when used with a house that at least has a garden hose, heat pump, sprinkler system, or some other type of continuous demand part of the time. Any house that only uses 320 gallons per day for sinks and showers would benefit from a "constant pressure" system only to eliminate water hammer and to reduce the size of tank needed. In Amtrol's "study" the longest water usage was 7 minutes. Constant pressure can only be achieved and is only needed when water is being used. A "cycle control valve" allows the use of a pressure bandwidth for intermittent uses and will then hold a "constant pressure" when water is being used for an extended period of time, such as with a tractor sprinkler.
Trying to hold a constant or unchanging pressure, a variable speed pump is unable to utilize any draw down from a tank. Every time the icemaker fills or a toothbrush is washed, a variable speed pump must cycle on and off. That is just one of the many problems with variable speed pumps, which requires other lengthy explanations.
Lab results in Amtrol's table #2 the "cycle control valve" reduced the cycles per day by almost 1/2 over the old pressure tank only system. 19 cycles per day was reduced to only 10 cycles when used with the "cycle control valve". That is a reduction from 6,935 cycles per year with old pressure tank only system to 3,285 cycles per year with the "cycle control valve" system, which is not a negligible amount. Because cycling is the main cause of failures on motors, pumps, pressure switches, and tank bladders, the "cycle control valve" can cut the number of cycles drastically which can greatly extend the life of all pump system components.
In the Amtrol lab "study" presented for the "house without a garden hose" the power consumed when using a "cycle control valve" is twice the amount as when using the old pressure tank only system. However, the difference between the one Kwh per day used with the constant pressure system and the 1/2 of a Kwh per day used with the old tank only system is only about 4 cents. 4 cents per day is only $14.60 per year. $14.60 per year is cheap insurance to get double or triple the life expectancy from your pump and related equipment.
In a real world application, which is a house with a garden hose, heat pump, sprinkler system or the like, Amtrol's lab results would show the devastating cycling that has long been the cause of pump system failures. A worst-case scenario would be a continuous demand of 7.5 GPM. Using a 15 GPM pump with a tank having 15 gallons of draw down as in Amtrol's "study", there would be continuous cycling every 4 minutes. That would be 360 cycles per day or 131,400 cycles per year. It does not matter if the old pressure tank only system saves any energy or not, the equipment would not last long enough to get a good test. Even if these continuous demands were only required 25% of the time that would still be 32,850 cycles per year with the old pressure tank only system compared to 3,000 cycles per year when using a "cycle control valve".
Using a "cycle control valve" the size of the tank needed can be greatly reduced. Larger systems that previously used multiple bladder tanks now need only one small tank. We do not expect tank companies to be happy about this new technology. The time, money, and effort Amtrol has spent to make a very one-sided "study" is itself proof that tank manufacturers are worried. Therefore, "cycle control valves" must be doing something right. If you want a realistic test for constant pressure systems, try a house that at least has a garden hose or a tractor sprinkler.
|1. Variable Speed Pump||Lab||31||1.026||58||69/42||11,315|
|2. Cycle control valve
w/ 20 gal tank, 15gpm pump
|3. 20 gal tank
w/o cycle control valve
|With continuous demand for 7 GPM||960||?||350,400|
* 10 day average; family of 4; 2.5 baths only 320 gallons per day, no garden hose, sprinkler system, etc.
One KWH is 8 cents. 1/2 KWH is 4 cents. A difference of 4 cents per day, $1.20 per month, or $14.40 per year. Would take 14 years to pay for extra $200.00 tank.
With any continuous demand such as sprinklers, heat pump, etc, KWH will be more with pump cycling on a standard tank than with Cycle Control Valve or Variable Speed.