Multifamily Energy Billing Solutions

Guest blog by Jim Brech with Accuspec Inc., ONICON Representative in New York, as featured on their website February 15, 2024. 

With the rising costs of energy and the push to be more energy-responsible, it has become even more important to provide accurate and repeatable BTU measurements for true energy consumption and billing purposes. Two markets that have seen a recent increase in the usage of BTU measurements are apartment and condominium complexes and retail spaces. Owners are interested in reducing their risks as well as providing an accurate bill based on a tenant’s actual energy usage. In this article, we discuss a multifamily energy billing solution.

Multifamily Energy Billing Requirements

In some areas, the law requires an owner to provide heat as part of their base services. Typically, however, they are not required to provide cooling, but in a fair number of cases, air conditioning is provided. How the owner bills for this energy use varies, but one method is to provide fan coil units that do both the heating and cooling. The owner then provides a BTU measurement as part of the fan coil unit with a programmable thermostat for temperature control.

BTU Measurement

Utilizing BTU measurement provides a win-win scenario as it allows the owner to bill the tenant for their actual usage. This encourages the tenant to be more energy-conscious. For example, a tenant is much more likely to raise the temperature during the warmer months while they are away from their apartment. This saves a tremendous amount of energy as well as ensures that the tenant has control of their comfort. How that measurement is made is important. The need for an accurate, repeatable, and low-maintenance BTU measurement is critical to ensure that the amount the tenant is paying is fair and accurate.

The old solution for BTU measurements was to have a Building Automation System (BAS) provide two temperature measurements (one supply, one return) and a flow meter. The data was brought into the BAS system, which calculated the energy usage and provided totalization. This method has several shortcomings some of which are the ability to operate when there are very low flow rates and low temperature differentials. Small signal errors or inaccuracies can result in very significant errors in BTU calculations. Let’s look at an error calculation using this method.

Energy Calculation Error Using a BAS

To simplify the example, this calculation only takes into account potential errors due to the temperature sensors, 4-20mA transmitters, flow meter and BAS (all other potential sources of error are ignored). The device errors are listed in the table below (sources of error are ignored).

Device Errors Using a BAS

Energy Calculation Errors Using a BAS

The Energy Calculation Error Solution

The ONICON System-40 BTU Measurement System provides a very viable answer to this problem. The System-40 is provided with an integral wetted inline ultrasonic flow measurement and a matched pair of platinum RTD temperature sensors. It is available in pipe sizes ranging from ½” to 2½” with flow rates from 0.03 to 250 GPM. The flow sensor is accurate to within ±1% of reading over a 25:1 turndown. The matched platinum RTD temperature sensors ensure a differential measurement uncertainty of ±0.18°F. The meter is also programable for both water and glycol systems. ONICON utilized CFD in the design of this meter, which allows for the meter to be used in most applications with no straight run, a critical feature for tight space installations such as a unit heater.

system-40 typical installation
        A typical installation for pipe size range from 1¼” to 2½”

The System-40 provides an analog output that is programmable for energy rate, flow rate, temperature (supply or return) or delta-T. The System-40 also is available with RS485 communication (BACnet® MSTP or MODBUS RTU). In addition, the ONICON System-40 is calibrated at the factory as a complete system and is “plug and play” once installed in the field, making start-up and commissioning much easier. Let’s examine the error calculation utilizing an ONICON System-40.

Energy Calculation Errors Using ONICON BTU Meter

The calibrated ONICON BTU meter drastically decreases the effect of errors in an HVAC system.

The ONICON System-40 is designed specifically to tackle this type of multifamily energy billing application. It simplifies and provides a proven, accurate, reliable and repeatable BTU measurement for both the building owner and the tenant. Visit the System-40 webpage for more information.