Solar Solutions Bristol Stickney, chief technical director, SolarLogic LLC, Santa Fe, N.M. Bristol’s Six Principles for Good Solar Hydronic Design
Case Study — A solar combisystem home retrofit
I
n June of 2009, we began designing a solar heating retrofit for an existing residence in the mountain foothills outside Albuquerque, New Mexico. This house
— seen on page 24 — has approximately 5,000 square feet of heated living space, and the entire building is heated with existing hydronic radiant concrete floors. The only heating fuel available is propane. The original conventional “hot water boiler” proved to have a voracious appetite. The own- ers wanted to cut back on propane consumption and to get better control over the energy efficiency of their home. Fortunately, the building is well constructed, with a reason- ably good level of insulation and heat retention. The large thermal storage capacity of the existing con-
crete floors allowed us to design a relatively large solar heating system into the building without any additional large water storage tanks, except for one 115-gallon domes- tic hot water (DHW) tank. Twelve solar collectors, pumped in groups of six, were installed on the house and, by October 2009, the heating system was converted into a solar combisystem and was ready for the coming winter heating season. In the photo, you can see that even though much of the roof is covered with solar panels, they are mounted in low profile to reduce the visual impact on the appearance of the building to a minimum. The other major components installed in this system are listed in Table 32-1.
Flow-center piping In many of my previous columns, I have described the
use of a primary loop that ties all the heating sources and all the heating loads together in a home heating system like this. I have used the “Combi 101” configuration that includes solar, boiler, DHW and warm mass floors to illus- trate this approach. In this retrofit, we use this same approach with a slight twist. The installers preferred using a Caleffi Hydrolink because it eliminates the need for assembly of the primary loop on the job site. The Hydrolink
Component
Solar collectors Water heater
Hydronic boiler
Hydraulic separator Solar heat exchanger Solar glycol circulators
Description
(12) Solarskies SS-40 (low profile mount, 75 degree tilt) (1) Oventrop 115-gallon dual coil (indirect) water storage tank (1) Triangle Tube Prestige 175 modulating/condensing boiler (1) Caleffi 2 + 2
(1) Triangle Tube TTP3-40
Heat distribution circulators (5) Grundfos UPS15-58 or similar Temperature controls Zone valves Thermostats Controls SL
Table 32-1: Schedule of Major Combisystem Installed Components Page 22/Plumbing Engineer
(2) Laing D5 Strong w/PV Module (Laing E1 installed in 2011) (2) Honeywell AM-102-US-1 Thermostatic Mixing Valve (8) Venstar 2-stage heating thermostats with adjustable deadband
(8) Belimo ¾" Latching zone valves LRB24-3 S SLIC Beta control system
2+2 model was configured to provide the same piping and heating functions that a primary/secondary system would have done. The result is a piping system that resembles a Combi 101 heating system with a more compact “flow cen- ter” and a larger number of collectors (12) and heating zones (8).
SLIC Beta system control and monitoring This heating system was originally designed with a con-
ventional control system using (8) Venstar 1045 two-stage heating thermostats, (1) Taco SR504 switching relay enclo- sure, (1) Taco ZVC404 zone thermostat/valve controller, (1) Taco ZVC406 controller, (1) Tekmar 155, (2) Tekmar 152 relays, and sensors. This control package is similar to the Combi 101 controls mentioned in an earlier column, with the added capability of night cooling control functions. Because of the owner’s proficient technical background and willingness to become a Beta test site, we redesigned the control system at the last minute during installation to include a Solar Logic Integrated Control (SLIC) system. The SLIC solar home heating control system has been
under development and Beta testing for a couple of years now. We designed it to replace all the relays and tempera- ture controls mentioned above by a single relay box with built-in software control. From the user’s point of view, it is simple to operate just by turning the room thermostats up or down. But internally, it allows us (and the owner) to moni- tor the performance of the heating system, measure and record its performance continuously in data files and adjust system settings locally or remotely over the Internet. This has proven to be practical, useful and informative, especial- ly during the first year of operation for this retrofit.
Fuel saving strategies for heating Twelve 4' x 10' collectors are installed, each capable of
saving as much as ½ gallon of propane on a clear sunny day. The
savings
achieved in this installation is not only from solar heat gain but also from the installation of high efficiency com- bustion and the addi- tion of heat saving control strategies, which can be moni- tored and adjusted as needed. Solar priori- ty over the boiler is
Continued on page 24 March 2011
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