The user override is madness

This week, I met with a HVAC project manager on a new large commercial tower. After I explained the shading controls specification and that we had been asked to provide the Tenant with an override to Shading Management Systems (SMS) automatic position, his response was not filtered:

“The user override is madness !”

He went on to explain; The HVAC system had been specified and delivered with the understanding that SMS will automatically operate the shades within the facade when in sun to avoid the majority of [external] heat gain within the floor plate. The HVAC solution was not capable to cool the space without the active Shading System. If the automation is overridden, the HVAC will fail to meet the ‘set point’ and use excessive amounts of energy which can potentially lead to system failure.

The user’s expectation to be able control the blinds and override the automation is a typical request. This is normally to benefit from the view, increase natural light levels and to maintain the feeling of control of their own surroundings. These are all fair and reasonable expectations.

Given the impact on cooling the building and the consequent increase in energy consumption, overrides must be managed and well thought through. The building must be able to operate as designed but this should not exclude the occupant’s needs. Compromise is possible with cooperation, understanding and intelligent application of technology.

1. The hard stance is to remove all local control and force the occupants to get used to the automatic processes. This sounds harsh but with training and education on the systems I have witnessed this work. Countries that have had earlier adoption of automated shading systems are more accepting of the solutions, people do start to get used to automatic functions (as witnessed with lighting and heating systems) BUT it is important the system works well.
2. A simple option is to allow an override to drive the blinds closed only and not open past the required heat management position. This has been proven and is an effective option that works. It is a compromise for the Tenant but is typically easy to apply and accepted.
3. Overrides can have simple timers applied, to have the automatic system take back control after a set time. Alternatively, the solution can have multiple levels of sun values (thresholds) with varying responses depending on the measured values. This is technically very effective but without a display or feedback to the user, this can create confusion.
4. With advanced Integration, the BMS (HVAC) can report when it is using excessive effort and SMS overrides can be blocked or limited.

Surveying the space and understanding the occupant’s expectations often reveals the blinds are being used outside of their intended purpose. Most cavity blinds are installed and controlled to manage and reduce heat gain, not glare, so if the Tenants expect to see their screens without discomfort this can create an issue.

For me, training and education on what the system is doing and the ‘why’ has the biggest impact. It is not fair to expect most Tenants to understand building physics however with good documentation, communication and potentially fine tuning of the automation the ‘want’ for user overrides can be reduced or removed.

User overrides and the associated logic can also vary across working areas or even down to individual shades, this limits the impact to the cooling system and offers flexibility. Ultimately the blind type and building’s dependence on the shading system are all factors that should be considered; however the likely solution is a mix of the above options with a view to keep it simple and easy to understand.

For the HVAC Project Manager we are working to find a compromise and will monitor the impact. The Shading Management System is adaptive, and we can change how these things work now or at any time throughout the building’s life.

Daren Whistler | ShadeLogik