Green Building

Green Building Energy Management Systems (Part 2) – A Design Guide

Green Building Energy Management Systems allow for centralised monitoring and control of energy use across building systems. Sensors throughout the building that measure conditions such as light level, indoor/outdoor temperature, and water temperature serve as data inputs for the BEMS, which uses that information to adjust control components such as dimmers, chillers, and boilers.

In our previous post we looked at what building parameters BEMS can measure. Let us now turn to how exactly this data is collected and how to handle the information. We will also outline the factors to consider when designing such systems.

Energy management systems range broadly in complexity. More complex systems have greater numbers of “points”—monitoring points (inputs) and control points (outputs)— which typically translate into higher energy saving potential, as well as higher installation costs. More complex systems are more fully automated and require minimal manual adjustment by building operations staff once the systems are operational.

As a rule of thumb, any building with a peak demand over 200 kW should consider employing a BEMS. Additionally, if an existing BEMS is over 12 years old, full system replacement should be considered. If the system is not quite that old, it may be advantageous to undertake a retrofit upgrade to a more sophisticated system, such as installing and connecting additional sensor and control points. The following table provides a rough estimate of the cost of new systems of varying degrees of complexity (valid for the USA as of 2011).

Cost of BEMS

 

Data Collection 

 

In order for a BEMS to perform optimally, one needs to come up with an accurate energy and water consumption profile for a commercial building. Some critical data measuring capability is required. The following is a recommended listing of the instrumentation that should be permanently installed in the facility.

  • Water meters
    • Municipality and/or well water supply lines to the building (if applicable)
    • Discharge lines from softeners and reverse osmosis systems
    • Main domestic cold water line
    • Main domestic hot water line
    • Main potable water line
    • Make-up line feeding cooling towers
    • Make-up line feeding steam boilers
    • Main irrigation water line
  • Energy meters
    • Across the water-side of chillers, evaporators, and condensers
    • Across each steam and hot water boiler
    • Across each solar hot water heating system
    • Across heat recovery equipment such as heat recovery steam generators
  • kWh meters
    • For each main distribution board
    • For each lighting and auxiliary power panel board above 20A rating
    • For each electrical equipment above 5 kW rating
  • Fuel/gas meters
    • For facility kitchen equipment
    • For each generator
    • For each boiler
  • Run hour meters
    • For each electrical equipment above 5 kW rating
    • For each air handling unit
    • For each boiler
    • For each water treatment unit
  • Flow/mass meters
    • Chilled and hot water in main lines
  • Temperatures
    • Approach temperatures for chillers, evaporators, and condensers
    • Boiler supply temperature
    • Air handling units air supply and return temperatures
    • Air handling units supply and return temperatures across chilled and hot water coils
    • Temperatures across heat recovery equipment
    • Space temperature for important areas (1/2 hour sampling)
    • Outside ambient temperature (1/2 hour sampling)
  • Pressures
    • Across each pump and booster set above 0.5 kW
    • Steam boiler outlet
  • Relative humidity
    • Space relative humidity
    • Outside relative humidity.

 

Factors to Consider

 

The first gauge of the type of BEMS that should be chosen is the energy spend of the building in question, which is what we have just looked at above. Now let us turn to other factors to consider when designing a BEMS.

  • Building Size

The size of a building generally can determine the overall energy spend, the types of equipment that is installed to heat and cool the building, the number of occupants, etc. As seen in the previous table, as we scale up the BEMS design, we increase the complexity of the system but also allow for better energy monitoring and therefore optimisation.

  • Geographic Location

It generally determines climate-related effects on energy consumption.

  • Number of Sites

When more than one building is involved, it should be a consideration that the BEMS can scale up and summarise the data from all sites as well as make comparisons of individual buildings.

  • Building Use(s)

A warehouse has different requirements than an office or school building which must consider things like occupant comfort. Occupant comfort while still managing energy is one of the most important considerations for selecting a BEMS. The BEMS should be able to normalise energy spend based on occupancy or determine the energy intensity of the building.

  • Type of Building

There are a host of considerations to be made based on the building type and age including the equipment that is installed, insulation, windows, lighting, digital capability vs. pneumatic, etc.

In this post we have looked at, in practice, how water and energy consumption should be measured in order to start designing a building energy management system. We have also looked at other factors that will affect the design options such as building size and type, and the intended use of it. Benefits of a BEMS include reduced operational costs, increased productivity, and more efficient operations. Every architect, engineer or building manager should consider incorporating one.

 

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