I’ve been hearing about “Constant Pressure Systems”; what does that mean? What do they do?
In the context of a residential water supply system, “Constant Pressure” refers to a combination of well, pump and control components designed to provide water to the home at a pressure that remains close to a chosen “set-point”, e.g. 60 psi, regardless of the amount of water (flow rate) being required at any one time.
A conventional design uses a pump, a tank with an air pre-charge in it, and a simple pressure operated switch. When the pump operates, it does so at its full rated power to drive water into the tank until the rising pressure causes the switch to shut it off. As you continue to use water, the pressure falls back down to the point where the switch turns the pump back on for another run cycle. This “pressure spread” is designed to be 20 psi. Tanks must be large enough to allow the pump to run for long enough to dissipate the heat in the motor generated by each startup (ideally about one minute).
A constant pressure system replaces the simple switch with a control (commonly called a Variable Frequency Drive, or VFD) and pressure sensor that together work to operate the well pump over a range of speeds, but always just fast enough to maintain that set-point pressure at the flow you happen to be using at the moment. All this is done electronically, in real time.
Why is this better?
In a nutshell, you get a stable pressure in the house, without the up and down cycling you experience with a conventional system. Many water using devices are happier that way; your shower, for example, but especially in-ground irrigation systems. But that’s just the beginning.
VFD controlled pumps use a 3-phase motor design (think industrial strength) that is inherently more efficient than single phase motor/starter designs. The control starts the motor “softly” to avoid the shock and heat inherent in the “full-on” start of a cycling system. Even better, the strategy of running “just equal to the demand” uses less power overall that the start/stop scheme. The reasons are complicated (maybe for a later blog) but in a nutshell, less power = less heat; less heat = less waste and less strain and wear on equipment. The net result is lower operating cost and better reliability.
For more information about the benefits of constant pressure systems and whether it could be right for you, call us at 603-868-3212 or visit us online at http://www.advancepumpandfilter.com/nh_pump_filter_constant_pressure_systems.php
News reports about PFC’s being discovered in both public and private wells at several locations well above the levels in the EPA’s Provisional Health Advisory have raised the level of concern among many home owners about the potential for such contaminants to be in their own wells. Recent reports of similar findings in surface waters and streams have heightened such concerns.
PFC’s, also referred to as perfluoroalkyl substances (PFAS), include a number of perfluoroalkyl acids (PFAA). Two of these, perfluorooctanic acid (PFOA) and perfluoroctane sulfate (PFOS) occupy most of the media attention, and are the specific subject of the Health Advisory. PFC’s have the useful property of repelling water and oils, making them very appealing to various industries. They are found in such diverse products as stain-resistant carpet and fabrics, waterproofing for fabrics and leather, some non-stick surfaces, and fire-fighting foam.
Both PFOA and PFOS have been shown to be widely distributed in the environment. They are persistent and do not degrade easily; they are also water soluble and are commonly detected in drinking water sources. The pathways for PFC’s to reach groundwater sources are many, and the understanding of the subject is very much an emerging science. They are associated with numerous health effects in humans, and developmental effects in infants.
How do I know if these contaminants are in my water?
PFC’s are not detectable through ordinary senses: taste, odor, color. They must be identified through testing by a qualified laboratory. The relevant concentrations are extremely small, in parts per trillion; that’s about one nano-gram per liter of water (ng/l). The Environmental Protection Agency (EPA) has developed Provisional Health Advisories for PFOA and PFOS at 70 ppt total, and are currently developing Lifetime (chronic exposure) Advisories.
So, I ran the test and I have some in my water – what do I do (if anything)?
We subscribe generally to the idea that guidelines developed by the EPA, and by extension State agencies, represent the best resource available to the public for evaluating the health risks associated with various contaminants. We do not, as a practice, make recommendations to treat contaminants that do not exceed EPA guidelines.
That said, we recognize that the maximum contaminant levels (MCL’s) for most health related contaminants represent a risk/cost/benefit assessment, and not a point below which no threat exists. Our belief is that each home owner should consider all available sources of information and weigh the reliability of each one. Essentially, it is the homeowner’s decision as to what level of contaminant is acceptable to them, and we understand that some may want to treat even for very low levels considered under the EPA limit. We are fully prepared to provide solutions to treat the issue.
How can PFC’s be removed from my water?
The treatment industry has been exploring a wide array of treatment alternatives. The consensus (and our own view as well) is that for residential treatment applications, there are two approaches appropriate for most scenarios:
- Granular Activated Carbon (GAC) is the go-to choice for both whole-house and point-of-use (drinking and cooking only) solutions. We follow the EPA/DES recommendation to use a pair of treatment vessels in series with a testing port between them to detect contaminant breakthrough while the second vessel is still effective. Size and specific choice of GAC type are application specific.
- Reverse Osmosis Systems, which also include activated carbon elements in the treatment path, can be an option where there can be an additional collateral benefit, such as salt reduction, nitrate, or arsenic remediation.
Any decision as to what to do about PFC’s in your water source has to start with the question “are they in there?” The tests involved are not inexpensive, so start by investigating whether your location is within a known contamination source or threatened by one. State resources, e.g. New Hampshire Department of Environmental Services (DES), may have that information; in some cases they may provide the testing if you are part of an area they are monitoring.
If, however, you “just have to know” then by all means have the testing done. One cost effective source we have located is Absolute Resources in Portsmouth, NH.
If you uncover a situation that merits treatment, for reasons satisfactory to you, call us! We will be happy to evaluate it, and recommend a cost effective solution suited to your needs. Click here for more information about our water testing services.