Five key considerations for need-based specifications

In my two previous blog posts, I described some of the issues of specifying technologies and making choices without considering the potential consequences (if you missed them, just click on the link to learn more). This time I’d like to share some tips on how to determine if your specification meets your need for a specific project. I recommend focusing on the following aspects:

1.      Minimum wire to air efficiency

·        Since some solutions are fully integrated, it can be difficult to specify a component efficiency. Instead, I would look at specifying a specific fan power requirement, which will be independent of fan size.

·        It should also be considered to require data for part load efficiencies of the system, as most systems run more than 99 percent of the time at less than 80 percent load. Different solutions vary significantly in part load efficiency, and this affects the building operating cost.

·        An example of a predefined load cycle can be found on slide 41 in this presentation from Europump. It's never going to be accurate, but provides a comparable benchmark for part load.

2.      Maximum allowable total footprint

·        Some air handling units (AHUs) based on EC fans actually require additional space outside the unit to secure a reasonably laminar air flow through the unit.

·        A compact AHU reduces transportation cost, but might not reduce total installed length.

·        The specification should include inlet and outlet requirements to meet proper airflow in the system.

3.      Control range

·        Determine the level of variation required in your airflow.

·        If you have high variations in occupancy, fan arrays might make sense, but other solutions are also possible and should be considered.

·        From an efficiency point of view, it might make more sense to use a larger plug fan, as the part load efficiencies are typically much better than on EC fans.

4.      Electrical installation

·        Link all variable speed devices to the same technical requirements for electrical installation performance.

·        If equipment such as AHUs are specified to include variable speed control, this will typically be stated in the mechanical specification.

·        This should always reference the relevant section of the electrical specification to ensure that the total installation meets the building requirements.

5.      Upgrades/repairs

·        For all key components there should be a specification for the maintenance, repair and replacement.

·        In many cases an EC fan solution requires the replacement of the entire fan module, with motor and electronics, no matter which part fails. In most cases replacement units have to be from the same manufacturer, as mounting and fan profiles are different.

·        In a system with discrete components, the motor bearing and any other part in the unit can be exchanged at a much lower cost. This reduces total cost of ownership, secures flexibility in choice of spare parts to multiple suppliers, and improves the sustainability of the project while reducing the environmental footprint, as only failed parts are exchanged.

·        Specifications should also be future-proof. If you decide later that you need a different communication protocol or additional hardwired signals, you will have the flexibility to integrate this.

These are just some of the things to keep in mind to ensure the optimum ratio between project cost, total cost of ownership and environmental impact. Feel free to mention other areas you would like me to comment on!.