Solar Solutions Bristol Stickney, technical director, Cedar Mountain Solar Systems, Santa Fe, N.M. Bristol’s six principles of good solar hydronic design Basic Combi-System Controls In this series of articles, I have been making the case that the key become my basic standard piping arrangement for over a decade for ingredients for solar/hydronic design and installation can be divided Combi-system 101. There are a number of additional benefits when into six categories, listed below, roughly in order of their importance. using this system in real-world installations. The primary loop is typ- 1. RELIABILITY ically installed horizontally, hanging from the ceiling. The swing 2. EFFECTIVENESS check valves must me installed horizontally or “flow upward,” since 3. COMPATIBILITY they may not close properly if installed “flow downward.” 4. ELEGANCE For the purpose of this discussion, I will present the very simplest 5. SERVICEABILITY control system that will provide the homeowner with Reliable and 6. EFFICIENCY Effective use of the solar heat available from this sample heating The success of any solar hydronic home heating installation system. Keep in mind, that as a simple example, it does not include depends on the often-conflicting balance between any of these six night cooling, baseboard heat, heat storage tanks for space heating principles. Finding the balance between them defines the art of solar or other relatively common options. Each additional option would heating design. require additional control components to be included in our wiring n previous columns I have introduced and explained some of the and control system. So to keep this article brief we will limit the dis- elemental concepts of hydronic solar home heating. Water tank cussion to the bare minimum heating system components using the heating, mass floor heating, thermostat control, glycol loops, bare minimum controls. I This type of system is typically installed with an economical num- combi-systems and flow centers have been discussed in earlier issues. These individual concepts are typically grouped together and ber of collectors that are tilted to maximize winter space heating. installed in every Solar Hydronic Combi-system that we have built With a limited number of collectors, all the solar heat can normally in the past five years or so. Of course, every solar home heating sys- be delivered to the cool mass of the radiant heated floors, or stored in tem was installed with the wiring and controls to make it work prop- the domestic water heater. If the collector tilt is matched to the sum- erly. Let’s take a closer look at a Primary Check-Loop solar heating mer load properly, all the solar heat available can be controlled by system and the controls that make it work. In this column I will dis- storing it in the domestic hot water tank and any excess solar heat can cuss the Solar Combi-system we most commonly install and the be dissipated to the floor mass without overheating the rooms. When Basic controls required for reliable operation. Please look online to properly designed and installed, this version of the Solar Combi-sys- review the previous columns in the PE and Phc News archives. tem can be about as simple, economical and effective as any active solar home heating system can be. This is because most of the heat- Primary Loop “Flow Center” Piping ing equipment (boiler, tank, radiant floors) had to be there anyway, In our region, the most typical Solar Hydronic Combi-system even without the solar collectors. includes a (1) solar heat collector array, a (2) gas boiler backup, a (3) domestic water heater and a (4) radiant heated floor. I introduced Basic Control Requirements this application in an earlier issue (spring 2009) as Combi-system A complete wiring diagram for the Combi-system 101 is shown 101, since I have installed these features so many times in home in Figure 14-2. This diagram is adapted from the control boxes that heating projects. This system includes only four items, two heat we have deployed on many similar installations. It contains a 2-stage sources and two heat loads and so presents a relatively simple exam- set-point control, a differential control, four relays (DPDT), a 2-stage ple for discussion. room thermostat for each zone valve, a zone valve control box, and The diagram seen in Figure 14-1 shows the configuration that has two pump control relay boxes. The models and brand names of the components are included for example only, and do not constitute an endorsement or recommendation. There are certain controls for this heating system that are required, and then some that are optional. Here is a short list of the most important functions. All the “required” functions are included in the components shown on Figure 14-2. Combi-System 101 — Solar Domestic Hot Water Tank Control (DHW) Required Temperature Controls • Low limit aquastat “AQ” (Usually comes with the hot water tank.) • Solar heat storage ON (Provided by Tekmar 155 differential control.) • Solar heat storage OFF (Provided by Tekmar 155 differential control.) • High Limit OFF (Provided by Tekmar 155 dif- Figure 14-1 Continued on page 34 Page 32/Plumbing Engineer September 2009 Solar Solutions Continued from page 32 • Solar heat source low limit (ON delay requires another temp. control.) Tekmar T152-1 Tekmar T155-1 • AC solar circulator instead of PV (Requires another differential HEAT CONTROL DHW STORAGE IN 10 A 10 A 10A 10A 155 152 24 V Only No Power 24V Only No Power control.) 1234 56789 1 2 3 4 5 6 7 8 9 On Power Com Src Stor Off CRRelay 1 Relay 2 Sen Sen Sen Remote Sensor C- R+ Relay 1 Relay 2 Sen Sen Sen Remote Sensors S3 T155-1-9 stor Tank} Combi-System 101 — Solar Heated Warm Mass Floor Zone S1 T152-1-1 HRF Heat Dump} & Solar Only} Drainback/Draindown S2 T155-1-8 src Solar HTX} Control STAGE 1 ENABLE DHW LOW LIMIT BOILER DISABLE CALL FOR HEAT HRF HEAT DUMP Required Room Temperature Control (Provided by 2 Stage 7 6 7 6 7 6 7 6 8 5 8 5 8 5 8 5 R1 R2 R3 R4 Room Thermostats) 1 4 1 4 1 4 1 4 2 3 2 3 2 3 2 3 • Auxiliary low limit “Stage 2” Heat ON (Backup or Auxiliary FLOOR HEAT END SWITCH HRF HEAT DUMP TSTAT HRF HEAT DUMP TSTAT BOILER PRIMARY HEAT ON) DHW STORAGE IN BOILER DHW HEAT STAGE 1 ENABLE DHW AQUASTAT • Minimum comfort temperature “Stage 2” Heat Off (Auxiliary 24 VAC OFF) CONTROL BOX COMBI 101 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 • Solar Heat Banking Allowed — “Stage 1” Solar Room Heat ON Boiler Call for Heat - DHW • Maximun comfort temperature “Stage 1” Solar Room Heat OFF 2 Stage Room Thermostats AQ Required Solar Collector Temperature Control T T T T BOILER CALL FOR SPACE HEAT DHW Aquastat (Provided by Tekmar 152, 2 Stage Set-Point Thermostat) ZONE 4 PRIORITY 24VAC MODE OFF NORMAL RESET • “Solar Priority” low limit (Solar Only ON, Boiler OFF, Heat ON N H TT T T TT TT ZONE 1 ZONE 2 ZONE 3 ZONE 4 Taco Taco 24 24 POWER IN SR501 R VAC SR501 R VAC COM COM Banking ON) Taco ZVC404 TT TT DHW-P3 Floor Heat-P4 MAIN EXTRA N/O COM N/C ZONE 1 ZONE 2 ZONE 3 ZONE 4 END END SWITCH SWITCH ZONE 4 RELAY 1 234 1 234 1 234 142 3 120 VAC 120 VAC Input Input 4 4 6 6 4 4 6 6 • “Heat Dissipation” high limit (a.k.a. Solar heat dump, Overheat NH 3 N/ON/C N/C N/O 5 NH 3 N/ON/C N/C N/O 5 protection) Features and Functions of the 101 Basic Controls DHW-P3 Floor Heat-P4 ZV1 ZV2 ZV3 ZV4 The 101 control system allows the warm floors and the DHW Figure 14-2 WARM MASS FLOORS tank to warm up more when it is sunny and less when it is not sunny, ferential control.) all within a comfort range that is programmable using the 2 Stage • Safety High Limit (P & T valve shown on the DHW tank in thermostats and Tekmar controls shown in Figure 14-2. As long as Fig. 14-1.) the floors and water tank are even a few degrees warmer than the Optional Temperature Controls for DHW boiler control set points, the boiler will not fire. This delay and pre- • Low limit aquastat priority (Requires another relay control.) Continued on page 36 ILD BU ING N C www.phpinc.us E O E U R N G C Precision . I S . L U TM U Hydronics SGBC ® CONTROL WIRING MADE EASY! Pre-wired Modular Electric Control Panels come ready for mounting with all the 120 VAC high voltage pre-wired. When used with PHP Mechanical modules, BoilerpaksTM and PHP Pre-wired Pumps, it provides a complete “plug and play” solution for up to six zones on a secondary loop, for controlling the primary loop pump and for prioritizing the DHW pump. For more information, visit w ww.phpinc.us and contact your distributor for a quote on your next project. 12/06 Precision Hydronic Products Division of JL industries, inc. 6807 NE 79th Court Ste E - Portland, OR 97218 Patent Pending Components Phone: (503) 445-4188 - FAX: (503) 445-4187 Made in the USA. ©2009 www.phpinc.us We do not export labor. Circle 22 on Reader Reply Form on page 65 Solar Solutions solar-only functions will stop, and the boiler will be allowed to take over.