Flagship solar combisystem controller: SLIC
By Bristol Stickney, technical director,
Cedar Mountain Solar Systems, Santa Fe, N.M.
In December of 2011, my company, SolarLogic LLC, reached a major milestone in solar heating control. At the MREA annual solar heating conference in Milwaukee, we announced the release of our Flagship solar home heating design and control system and demonstrated it to the solar professionals there. Figure 43-1 shows the control box and a hands-on display with a home heating simulator used for demonstration and training. For the past three years, we have been working quietly on a new way to design, deploy and control solar combisystems. Our intention is to take the guesswork out of solar heating design and control, so that even a complex solar hydronic combisystem can be deployed rapidly and controlled in a standard and predictable way by any qualified heating professional.
This has involved development of a software design package known as the SolarLogic Assisted Solar Heating Design (SLASH-D) and an all-inclusive heating system controller called the SolarLogic Integrated Control (SLIC). After several years of research and development, testing in our hydronic heating lab, Beta testing in solar homes in diverse locations, writing software for both design and control, acquiring four U.S. patents and packaging all this into a single control box, we have now released the fruits of this work for use in solar heating projects. The most recent product offering is known as the SLIC Generation II. It provides smaller buildings (less than 10,000 sq ft) with the benefits of a commercial energy management and control system, but without the high software and hardware costs common to those custom installations. Here is a brief summary of how it works.
SLASH-D (SolarLogic Assisted Solar Heating Design)
As the name implies, this design software is intended to assist a solar heating professional to design a whole-house solar combisystem by using a standard piping configuration that is compatible with a standard control strategy. The SLASH-D requires a minimum amount of information about the job, such as the heated square feet, the number of zones and the size of the DHW hot water load. The heating load of the house is quickly estimated, based on the weather/location and either the known heat loss from the house or an automated estimate of heat loss based on the type of construction (poor, average, well-built).
The program will then suggest the number of collectors and a recommended tilt based on the desired level of solar heat contribution (low, medium, high). The user can change the number, size and tilt of the collectors and watch the monthly fuel savings change in response. The program displays piping diagrams of all primary and secondary plumbing and suggests a list of parts, and the diagrams change in response to the users input. Many outputs and recommendations have an “override,” so more experienced users can try other alternatives quickly.
All the piping and components are compatible with the SLIC control system. In fact, once the basic layout of the heating system has been accepted by the owner and installer, the output files from the SLASH-D design process become the input files for the SLIC controller, so that it “knows” what components are in the heating system without any further programming by the installer at startup. The system files can be provided to the SLIC on its built-in removable SD memory card or transferred to it directly through a network connection.
The SLASH-D is intended to take the guesswork, the “special solar knowledge” and the seemingly endless plumbing variations out of the design process for smaller solar heated buildings (less than 10,000 sq ft). It also automates the process of creating a sophisticated control system that is matched to the needs of the solar heating installation from its very inception.
SLIC (SolarLogic Integrated Control for solar combisystems)
The SLIC control replaces the need for all conventional controls commonly found in a hydronic heating system along with all the common solar controls. So, for example, in one recent installation, the solar heating system was originally designed with a conventional control system using eight Venstar 1045 two-stage room thermostats, one Taco SR504 switching enclosure with four pump relays, one Taco ZVC404 room thermostat/zone valve controller, one Taco ZVC406 thermostat/zone valve controller, one Tekmar 155 solar differential thermostat, two Tekmar 152 set point controllers, many relays and many sensors. During installation, this parts list was abandoned and replaced with one SLIC control box and eight SolarLogic room thermostats. All the pumps, sensors, thermostats and zone valves are wired directly to a single point of control. When all the wiring makes a home run to a single box and all the terminals are clearly labeled, the installation becomes much easier.
The SLIC can control solar and backup heat sources over 10 heating zones, domestic hot water, heat storage tank, both a pool and spa and ice-melt. It uses a Vortex flow meter to calculate Btu solar contribution, monitors both glycol pressure and boiler water pressure and offers a pH meter to monitor the state of the glycol. The built-in software control algorithms incorporate our experience from hundreds of solar heating installations spanning the past 30 years. Basically, the software does what I would do if I were in the boiler room watching over the system.
From the user’s point of view, it is easy to operate by simply turning the room thermostats up or down. But, internally, it makes sophisticated energy-priority decisions that mimic multiple differential thermostats and two-stage set point thermostats working in concert. Datalogging is built into the system, which records everything happening to the heating system continuously at over 200 data points in data files that are compatible with spreadsheet display. The owner, the installer or SolarLogic technical support have the capability to inspect the performance (past or present) and diagnose or adjust the system remotely. This eliminates call-backs and has proven to be practical, useful and informative, especially for fine tuning the balance between comfort and efficiency for the solar homes where the earliest systems have been installed.
The control system can be accessed from any computer, either plugged into the SLIC directly via an Ethernet switch, over the local area network (LAN) in the house or over the Internet. Access is protected by passwords and other security measures. A typical view of a SLIC display page is shown in Figure 43-3 which shows room thermostat details as an example. Display pages can be tab-selected and displayed on any computer from any location (with the right password and a connection to the network) and used for remote scrutiny and adjustment.
Table 43-1 shows an abbreviated list of the control functions built into the SLIC control system. All of them are adjustable through software for optimizing the performance of the house. Features that are not needed are simply turned off by the system software at the time of installation.
Bristol Stickney has been designing, manufacturing, repairing and installing solar hydronic heating systems for more than 30 years. He holds a Bachelor of Science in Mechanical Engineering and is a licensed mechanical contractor in New Mexico. He is the chief technical officer for SolarLogic LLC in Santa Fe, N.M., where he is involved in development of solar heating control systems and design tools for solar heating professionals. Visit www.solarlogicllc.com for more information.