4 FM quick reads on HVAC
1. Optimize Heating And Cooling Source Equipment To Increase HVAC Energy Efficiency
Today's tip from Building Operating Management comes from Daniel H. Nall of Flack + Kurtz. With the HVAC system's air and water distribution systems optimized, the heating and cooling source equipment can be optimized. There is a basic conflict between optimizing the efficiency of the distribution systems and optimizing the efficiency of the heating and cooling source equipment. For the distribution system, hotter hot water and colder chilled water can result in a greater temperature differential across the system, resulting in lower required flow and lower transport energy consumption. For the sources of heating and cooling, however, cooler hot water and warmer chilled water result in more energy-efficient production of these resources. Optimization of these conflicts will result in the most energy-efficient systems.
For both boilers and heat-pump-cycle heat sources, lower hot water temperature results in greater efficiency. Lower hot water temperature allows the utilization of condensing boilers and even lower hot water temperature increases the efficiency of the condensing boiler. Maximizing the efficiency of the entire system relies upon maximizing the thermal coupling between the distribution medium, air or water and the end use, the conditioned space. The key to optimal efficiency heating is thus close approach heating coils, or extended surface area convectors or radiant panels. By reducing the temperature differential between space and distribution medium (air or water), temperature differential across the transport system can be maximized while maintaining a lower-temperature heating source.
2. Data Issues Are Critical With Fault Detection And Diagnostics (FDD)
Today's tip from Building Operating Management comes from Jim Sinopoli of Smart Buildings LLC. Facility managers who are considering fault detection and diagnostics tools should be aware of the importance of data and network issues. Here are some points to keep in mind.
Lack of Data. Fault detection and diagnostics tools rely on data from building automation systems. If there are not enough sensors, if the sensors are inaccurate, or if the building has a legacy control system and for some reason accessing the BMS database or controllers is difficult, there can be issues with obtaining the accurate data required.
Using the Diagnostic Data. Many of the fault detection and diagnostics software tools can provide information to the technician or engineer regarding potential corrective actions. This information needs to be integrated into the work order system, which may be one application in a whole suite of facility management applications, in order to use the information effectively.
Applications in the Cloud. Many companies offering fault detection and diagnostics software will provide the application on the client site, but have an option to provide the application as "software as a service" (SaaS) or in "the cloud." Essentially the vendor hosts the application, and the facility manager accesses the application through a normal web browser. This can be an issue with many corporate IT departments because of the need to pierce the corporate IT firewalls and security to get to the BAS data the application needs.
Prognostics Data. While fault detection and diagnostics tools seem inherently capable of providing prognostic data — that is, it can analyze fault conditions or degradation faults and predict when a component will fail or not be able to perform correctly — very little has been developed in this area. In addition, prognostic data would allow for more proactive, condition-based maintenance, which would be a different approach for facility management organizations that are reactive and corrective.
3. 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."
4. 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.
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