Is VRF right for a K-12 school?
The VRF system is uniquely suited to address the changing K-12 environment and is rapidly growing in popularity. By 2012, DXS had K-12 schools operating successfully with Daikin VRV/VRF systems in all of our major markets (Houston, Austin, San Antonio, Dallas) and other Daikin reps had the same in their markets.
The layout of a school breaks down the building’s total capacity into zones typically between 1.5 to 3 tons (excluding OA), just the right capacity for a Daikin VRV/VRF system. Each of these classroom zones must be able to operate with a widely varying load (as people come and go) and even as an individual zone when the full building may not be occupied. That’s not possible with a traditional chilled water system because the central plant has to run to turn air conditioning on in any portion of the building to accommodate even one person working after hours.
The second major driving force is energy and water consumption. While air cooled chillers and electric heating systems are reasonably cost effective, they are not energy friendly. In the last five years as LEED and other “green” building programs have become the norm, we have seen many school districts change their design strategy to reach higher efficiency goals. A VRF system provides an avenue for school districts to improve energy efficiency without driving construction costs higher and without a substantial water consumption increase.
What about all the filters and drain pans?
While it’s true that in a VRF system, the filter changer will have to make the rounds through the building to each system, this is a fairly simple task. To make this easy, care should be taken to make filters easy to access in schools (cassette style units, for example, are easily accessed at the ceiling). Design engineers should not locate filters deep into ceiling plenums or above light fixtures because will make regular changes challenging.
For drain pan maintenance, outside air ventilation should be addressed. When applying VRF to a school, if the ventilation air is brought directly into the VRF fan coil unit, then the condensate maintenance will be similar to chilled water fan coil systems or unit ventilators. For this reason and for humidity control reasons, it’s best to design K-12 VRF systems with a dedicated outside air system. A properly designed ventilation system can substantially reduce or eliminate the amount of condensate that is generated in the VRF fan coil units.
How do you apply VRF in gyms at a school?
A typical VRF fan coil unit is not always the best solution for large gyms because VRF systems are ideally suited for zones with four or less tons. Where we have provided design assistance for existing VRF schools, the gym areas are designed with DX rooftop systems or central station air handling units with DX coils. These systems are not VRF, but when Daikin rooftops and air handling units are used, they can be seamlessly tied into the same central control network.
It is now possible to design a customizable air handling unit and tie the DX coil to a high-efficiency VRF condensing unit. For rooftops 15 tons and smaller Daikin has already released a “VRV/VRF in a box” Rebel rooftop that uses the Daikin VRV/VRF inverter compressors and much of the same technology that you find in a VRF system. These products have best-in-class energy efficiency levels to maintain the high performance expectation that you would have with a Daikin VRV/VRF system.
What about the outside air?
How to handle the outside air load and humidity are among the most important design criteria on a K-12 project. In a K-12 classroom, a dedicated outside air system (DOAS) may be best. In any hot and humid climate, the DOAS can decouple the temperature control from the humidity control. The DOAU is often designed for dehumidification capacity and controlled by a zone level humidity sensor. In a K-12 school, the DOAU would be the primary dehumidification system and the VRF system would be the temperature control system.
The best system for this strategy is a desiccant based dehumidifier that provides a neutral temperature supply at a suppressed dewpoint of between 45 – 47 degree dewpoint. At this low dewpoint, the ventilation air being delivered to a classroom will dehumidify the ventilation air load and can provide additional drying effect to the humidity sources already in the classroom. This strategy nearly eliminates the condensate in the VRF fan coils and greatly reduces long-term maintenance required for the condensate piping.
This stuff is too complicated for my district’s technicians.
That’s a common misperception. The Daikin VRV/VRF system’s hardware is actually straightforward. It has a fan coil, a condensing unit, and a branch selector when heat recovery is used. That’s it! In our classroom service technician training classes, students are surprised at how “simple” the inside of a Daikin fan coil actually is.
The “sophistication” of any HVAC system is in the controls setup. This is nothing new for K-12 operations people, who already work with third-party building automation system (BAS) controls providers to program and manage controls for chilled water systems. The primary difference between a third-party controls system and a Daikin VRV/VRF system is the “plug and play” nature of the VRF system. Each component has a factory circuit board. These boards do not require field programming, modification, special software or anything else to install and maintain. A base level technician is qualified to drop in a replacement circuit board and reconnect the factory quick-connect wiring harnesses and bring a system back online.
To assist school districts in taking care of their buildings, DXS offers a six-hour technician/operator training class that focuses on how the VRF system’s controls are set up and how the system operates. At the end of the class, students have a much higher comfort level and understanding of the “magic” inside of a VRF system.
For the majority of Daikin VRF customers, basic system maintenance of fan coils, thermostats, control boards, etc., are looked after by the local maintenance department personnel with the completion of a one-day orientation and service training class. As typical with most major equipment, condensing unit maintenance is often performed by DXS’s factory trained VRF technicians or by another service contractor’s technician that has completed more in-depth service training.
Does this work with my BAS (Controls) system?
Yes. The Daikin VRV/VRF systems can be provided with a gateway interface to any LON or BACnet platform. This gateway makes a wide range of data and control points available to the controls programmer for the integration.
Additionally, Daikin has a factory-native central controller option that can be wired into the VRF system. This Daikin central controller can provide several advantages by delivering many functions of a common controls setup in pre-built package. This allows the owner/operator/controls programmer to simply “fill in in the blanks” for setpoints rather than having to provide the “start from scratch” programming logic that is required to complete a third-party interface.
On larger projects it’s common to have both the Daikin native central controller and a BACnet Gateway. The Daikin controller provides much of the base functionality, including setpoint temperature range restrictions, heat/cool changeover logic, and even demand controlled ventilation when using a Daikin outside air unit. The BAS provider would provide the schedules and integration of the HVAC into other equipment or systems in the building. While nearly everything that can be done on the Daikin central controller can be provided by the BAS company, it would require much more programming, setup, testing, and commissioning time to complete.
How do I find someone to install this system?
There are more than 25,000 VRV systems installed in North America and several hundred in the DXS territories. There are well over 500 individuals (as of 2012) who have completed Daikin VRV/VRF installation training classes and nearly every major commercial contractor in Houston, Dallas, San Antonio, or Austin has installed at least one VRV/VRF system. Your local DXS sales office will gladly provide a recommended contractor list.
Local installation and commissioning classes are also taught monthly if you have a preferred contractor. DXS provides meticulous oversight for VRF system installations to ensure that the contractor, owner, architect, and engineering firms all have a successful experience when using Daikin. The DXS technicians and contracting sales teams work hands-on with our contractor customers to support their purchase of Daikin VRV/VRF.
What if I need parts/service?
DXS is a full service “applied system” rep company with VRF expert sales professionals who provide design and engineering assistance to make sure your system is designed and installed correctly. DXS also has a full service parts and service division in each of our local offices to provide immediate and often same-day service response to customers. Additionally, many of our contractor partners are trained and qualified to provide service for your systems. Our parts and service people can assist in all aspects of long-term maintenance. We are able to provide full-service maintenance contracts or training and parts sales for clients that wish to handle their service needs themselves. Contact your local sales office with any questions about parts and service for your building.
A word of caution: The availability of parts, service and application experts in the VRF market varies greatly among manufacturers. Some VRF manufacturers have chosen to go to market through a distribution-type channel where VRF is sold “across the parts counter” much like a contractor would purchase a standard DX split system. In this model, the installing contractor has complete responsibility for installation, warranty and service support. There is not a factory service office in most cases and can be risky for an owner because qualified service support will be out of town and often subject to a several week delay.
Is a VRF system more expensive than a traditional system?
It’s actually not when used in the right context. A VRF system is not intended to be the absolute cheapest cold air you can buy, but it is competitive with systems of similar features. Our sales people are well versed at explaining the cost points of a VRF system and configuring a system to meet the budget expectations for our clients (we don’t over-engineer systems). We have worked directly and closely with Daikin on product development to optimize VRF for the Texas market. In addition, in the years since 2007 when the product first gained momentum, training for local installation has expanded and the knowledge base has grown among installers, which has led to lower installation prices.
With that said, there are several design decisions that can change the cost point of a VRF system quite significantly. To better understand the cost points for a Daikin VRV/VRF system, contact your DXS sales representative.