4 FM quick reads on HVAC
1. Unexplored Potential in HVAC Systems
When it comes to making changes to save energy, building owners like to see low-cost or even no-cost measures. Many of these smaller fixes are relatively obvious to a third-party set of eyes with design and operational experience (perhaps hired to perform an energy audit), but may be missed by those "in the trenches."
So before you start replacing expensive equipment, work with your building engineer or maintenance technician, and conduct an audit to make sure your existing equipment works properly.
Some of the simple things you may find include:
- Variable frequency drives that were set on bypass because of a problem with the drive. We often find drives running at the full 60Hz because they have never been returned to their proper automatic action state.
- Economizer dampers in a particular fixed position because of linkage or drive motor failures.
- Outside air dampers with a 2-by-4 wedged into them to keep them open because of the same control failure as above.
- Dirty primary or secondary filters cutting down on proper airflow.
Probably the most underexplored area, though, is thorough examination of the hydronic coils, primarily the cooling coils. Cooling coils, especially those with tight fin spacings, oftentimes act as filters, trapping not only particulate but also biological masses on the fins. This not only impedes the proper volume of air getting through the coils and thus to the spaces served by the HVAC system, but also reduces the heat transfer of the system, causing the compressors to work harder and thus use more energy. And it's the biologicals that can lead to that unpleasant "dirty socks" smell. So, proper cleaning of the cooling coils can not only save energy but also improve IAQ and IEQ. Please note the emphasis on "proper."
2. Improve The Efficiency Of The Heating And Cooling Distribution System
Today's tip from Building Operating Management comes from Daniel H. Nall of Flack + Kurtz. After available environmental resources have been fully exploited to reduce heating and cooling requirements, the next strategy is to improve the efficiency of the heating and cooling distribution system for the building.
One approach to reduced transport energy is to utilize water, to as great an extent possible, as the heat transport fluid for the building. Transport of heat by water is 4 to 10 times as energy efficient as transport by air. The trade-off for reduced transport energy, however, is the decreased effectiveness of free-cooling strategies in water based distribution systems. All water distribution systems, therefore, will be most effective in extreme climates, those that are too hot and humid to provide free cooling, or so cold that waterside free cooling is frequently effective. For these climates, a dedicated outdoor air system with heat recovery, for ventilation and dehumidification, along with a primarily hydronic sensible heating and cooling distribution system, such as fan coils, chilled beams, or radiant panels is likely the most energy efficient system selection.
For peak load operation, the efficiency of distribution systems can be significantly improved by minimizing the pressure drop against which the system must operate. For hydronic systems, pipe sizing and selection of valves is critical for minimizing flow pressure drop. Similarly, for air distribution systems, duct sizing, selection of aerodynamic flow accessories — such as turning vanes — and optimal sizing and selection of dampers are critical to minimizing pressure drop. Coils and other heat exchangers should be selected for reduced pressure drop on both the primary and secondary sides of the exchanger. Minimized approach temperature should also be considered in the selection of coils and heat exchangers. The ideal distribution system, whether air or water, should feature reduced pressure drop along with maximized temperature differential across the system.
3. With Fault Detection And Diagnostics (FDD), Take Close Look At Buildings, Software Capabilities
Today's tip from Building Operating Management comes from Jim Sinopoli of Smart Buildings LLC. As promising as fault detection and diagnostics is, facility managers need to take a close look at their buildings and at the capabilities of available software tools before rushing out to install a fault detection and diagnostics application. Consider these issues.
Handling Fault Information. Facility management organizations need to decide how best to handle the fault detection and diagnostics information. A "fault" identified by a fault detection and diagnostics application indicates that the system is not performing optimally. This is different from a system alarm indicating some criticality and need for immediate action. In many facility management organizations, both alarms and faults automatically trigger a work order, but do so identifying different priorities for the work order. Other organizations set the faults aside and then periodically meet to discuss the remedies.
Rules Specific to Building Systems. The rules apply to specific HVAC relationships and equipment, and facility managers need to be assured that their specific building systems are or can be addressed by the fault detection and diagnostics software application. Many products start with a standard set of rules, which may address similar or smaller buildings or HVAC configurations, and then add rules developed by others or by the end users themselves.
For larger buildings, fault detection and diagnostics does not come right out of the box. Almost every sizable building and HVAC system is slightly different, so the rules have to be customized. That's not necessarily a bad thing as the customized rules are likely to be more accurate and based on specific building needs, but customization requires additional installation time.
Lack of Applications for Emerging and Other Systems. Fault detection and diagnostics applications are primarily HVAC-focused. There is an opportunity for the industry to take the rules-based approach to other systems, such as solar, wind, geothermal, or power management.
Alternative Ways to Deploy Capability. Fault detection and diagnostics is simply a software application. At some point in the future, control and equipment manufacturers will simply integrate fault detection and diagnostics software routines into their controllers.
4. Use Economizers To Reduce HVAC Energy Use
Today's tip from Building Operating Management comes from Daniel H. Nall of Flack + Kurtz. Facility managers looking for opportunities to reduce HVAC energy use should focus on airside and water side economizer strategies.
The first step to reducing HVAC energy consumption should be to make use of available environmental resources to help meet heating and cooling loads. These resources might include the outside air during portions of the year in many climates.
In the northeast, north central and in much of the west coast of the United States, the ambient outside air often has a lower enthalpy than does the interior room air. In such conditions, air returned from the occupied space can be dumped in preference for the lower enthalpy outside air, reducing the energy required to cool the supply air to the conditions necessary to maintain room temperature and humidity setpoints. This strategy is called airside economizer.
In buildings without sufficient architectural access to outside air, cooling towers can be used to make cold water when exterior conditions permit, providing chilled water without the energy penalty of refrigeration compressors. This process is called waterside economizer. Other resources that can be used to offset heating and cooling in the building can come from the building itself. Heat and moisture recovery from exhaust air can be used to temper incoming outside air, reducing the amount of energy required for heating when that outside air is very cold or cooling when that outside air is very hot or humid. Heat recovery can be a very effective strategy when high ventilation or exhaust rates are required, either because of occupancy or contaminant control.