water sub-metering

Tapping into water savings

Why equipment scrutiny is vital when comparing water sub-metering solutions
Wednesday, December 7, 2016
by Mike Kazmaier

Many building owners today are familiar with electricity sub-metering and its proven energy and cost savings. However, few understand that much of the regulatory oversight that makes electricity sub-metering services easy to compare aren’t applied to water sub-metering.

The equipment used for electricity sub-metering is rigorously tested by Measurement Canada before approval and sealed by a Measurement Canada (MC) certified sealing house before installation. Water sub-meters are tested initially by the manufacturer, but third party meter sealing for water sub-meters is not required. Measurement Canada also requires that electricity sub-meters be independently inspected after installation, but this is also not required for water sub-metering systems and is left up to the sub-metering service provider.

When it comes to water sub-metering, equipment selection often involves ensuring it conforms to the American Water and Wastewater Association (AWWA) C-700 standard, which recommends tolerances and accuracy requirements for water meters.  Unfortunately, despite this standard, there can still be large differences in water sub-metering equipment and the impact it can have on a building owner’s bottom line.

Comparing water sub-metering technology: a case study

At Clean Cut Energy (CCE), we believe referencing each water sub-metering service to a benchmark is a critical part of the process. The reference we use is how effectively the sub-metering equipment in a building recovers the utility costs from its residents. By tracking the utility “recovery rates” of all the buildings we service, we were able to determine that some of our ‘inherited’ water meters were recovering less water from residents than the water meters we typically choose to employ. Below are the results of our in-depth investigation.

Figure 1. (below) depicts the average difference in recovery rate observed between inherited water meters and the water meters typically used in our buildings.

recovery-rate-graph

Differences in accuracy

This investigation by CCE engineers found two interesting differences in the water meter technology we compared. Table 1 (below) shows the AWWA C-700 standard requirements for water meters, and compares it against the specifications for the two water meters used in the study. What’s notable is that despite both being ¾” meters, meeting the minimum low flow water consumption value specified by the standard of 0.5 USgpm (US Gallons per minute), the variation between the rated low flow measurements is more than 1500 per cent. This is the result of both differences in the technology and the low flow accuracy.

table-1

Table 2 and 3 (below) show the average capital cost difference of these two meters and what is the estimated lifetime cost of using the lower accuracy meter vs. the high accuracy meter, based on an eight per cent difference in recovery rate.

The incremental equipment purchase cost difference for a 200-unit building is $16,000.  The lifetime cost of this decision is over $400,000 with a Net Present Value of $160,000 to the building owner today. This illustrates how cost-cutting decisions made by a sub-metering supplier may result in expensive lifetime utility costs for the building owner.
In a building with very little common area use and no leaks, CCE sub-metering systems are able to recover upwards of 97 per cent of the incoming water purchased by the building from building residents, which amounts to a 10-fold return on invested capital for the building owner.

graph-2-and-3

The problem with pulse meters

Table 1 (top) highlights another significant difference between the two meter types.  Meter #1 uses pulse output as the form of communication technology. This means that when a predetermined volume of water has passed through the meter, a pulse is produced that is picked up by an attached listening receiver. Meter #2, by comparison, uses an encoder level read that means a communication protocol asks the meter for its reading and the meter has to reply with the data which includes the entire meter reading and the meter serial number. This also means that when a reading is requested the returned value is the same value that is displayed on the top of the meter dial.

Why it matters

The simple answer is ‘fault tolerance’. With Meter #1 consider what happens when the receiver no longer receives pulses from the meter. In this case the sub-metering service provider has a question to answer. Did pulses stop arriving because no water was consumed in the unit or because the wire was broken and the pulses weren’t received?  The fact that this system does not definitively disclose when it is in a fault state is a significant problem. Meter #2 however will immediately indicate when it is in an error state because communication was attempted and no reply was received. There is no ambiguity in this circumstance and a repair must be performed.

Consider also a scenario where the receiver doesn’t get all the pulses sent from Meter #1. This can create a discrepancy between what the meter dial indicates (since the pulses were sent) and the water use that appears on the customer’s bill (what the receiver picked up). The only way to discover if this error is occurring is to audit a number of meters yearly and compare the received pulse values (shown on the bill) to the meter dial reading.  In the meantime the resident is likely being under billed for their usage and the owner of the building is on the hook for this undocumented water use until a suite by suite audit is performed.  Meter #2, by comparison, will never have this issue since a request to the meter returns the actual meter reading. No discrepancy is therefore possible.

The faults associated with pulse meter readings give rise to what we refer to as pulse meter recovery rate erosion. This occurs when pulse meters slowly fail and the recovery rate that started high when they were first installed continually decreases relative to the total water consumed by the building. A high functioning pulse water meter system requires significant ongoing yearly building maintenance and auditing. We believe that making the decision to invest in high accuracy encoder read water meters is based on easy math.

Questions to ask when selecting a water sub-metering partner

It’s important to ask for both references and meter specifications. When talking to references, ask for samples of some of their building recovery rates. Don’t settle for samples from new buildings they just commissioned, ask for ones that are at least five years old and make sure they can show you results down the road that meet your expectations. Working with companies that select high accuracy equipment that is properly suited to your building is not only the water wise thing to do, but it is also the best way to make sure building owners get the maximum return from a sub-metering system. That is something that our engineers don’t question.

Mike Kazmaier, P.Eng is the Director of Operations at Clean Cut Energy Corp, a nationwide Tier 1 water, electricity and thermal energy sub-metering firm. To contact Mike please visit [email protected]

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