CONIFER SOLAR CONSULTING

Jon Klima, Owner
360 Trout Lane, PO Box 23, Guffey, CO 80820
Phone: 719 479-2281,  Email: jon.klima@gmail.com
In business for 37 years

 

• Article 21 - February, 1997

 

Programmable Differential Temperature Controllers©

 

This is the eight in a series of articles that will summarize the programming capabilities of. Most of the differential temperature controllers used in the Colorado area. This article will examine the dual output Novan 2011 and DLP-20 controllers. From a control and logic standpoint, the 2011 and DLP-20 are the same. The 2011, which proceeded the DLP-20, is a single box unit. The high voltage (120 VAC) and low voltage (logic and control) are all on the same circuit board. The DLP-20 consists of two circuit boards, each contained in its own box. The high voltage terminal board and control relays are in one box while the logic and temperature display are in the second box. The two boxes are connected by a five wire umbilical cable. The early 2011 models work with 3 K ohm sensors but later 2011s and the DLP-20s work with 10 K ohm sensors. Unfortunately, not all 2011s are marked with the type of sensor that is required and it is only by trial and error that you can determine which to use.

 

The programming capabilities of these controllers are minimal. The controllers are designed to control the collection of heat from a collector array and deliver the heat to either of two loads, i.e., a spa (or bulk heat storage tank) or a solar DHW tank. You can program which load gets heated first and how high a temperature it should be heated to before switching to the second priority load. There is a bit of a quirk that frequently occurs here, however. Assume the priority switch is set to DHW, the spa sensor is at about 90° F, well below its set point of 102° F, the DHW sensor is at 130° F, and the collector sensor is at 110° F. Although the priority switch is set to DHW, the spa is asking for heat and the collector can supply it. So the controller will switch the output relays to provide for spa heat collection. This will keep the collectors from heating to a high enough temperature to provide heat to the DHW. Only when the spa is satisfied or the collector to DHW turn ON differential (usually about 16° F) is reached (by either cooling the DHW or heating the collector) will the controller switch to the DHW heat collection mode.

 

If you, even occasionally, need to check out a 2011 or DLP-20 in the field, I suggest you go to an electronic parts store and buy one each of the following 1/4 or 1/2 watt resistors; 560 ohms, 1 K ohm, 1.8 K ohm, 3.3 K ohm, and 6.2 K ohm. If you are dealing with a 2011 controller that uses 3 K ohm sensors, connect the 1.8 K ohm resistor to the spa sensor terminals, the 560 ohm resistor to the collector sensor terminals, and the 1 K ohm resistor to the DHW sensor terminals. You should obtain temperature readouts close to 99° F, 155° F and 125° F respectively. If the 2011 uses 10 K ohm sensors or you are dealing with a DLP-20, connect the 6.2 K ohm resistor to the spa sensor terminals, the 1.8 K ohm resistor to the collector sensor terminals, and the 3.3 K ohm resistor to the DHW sensor terminals. You should obtain temperature readouts close to 97° F, 156° F and 126° F respectively. If the temperature readings are more than about 5° F off, there is probably a problem with the controller. If the readings seem OK, place the priority switch in the DHW position and the DHW TEMP adjustment knob fully CW. Then rotate the SPA TEMP adjustment knob fully CCW, then CW. The controller should continue to give a DHW heating output. Now, short out the DHW-HL sensor terminals. The DHW and SPA output LEDs should both be off. Remove the DHW-HL sensor terminal short. Now rotate the DHW TEMP adjustment knob CCW to about the 9 o'clock position. Then rotate the SPA TEMP adjustment knob fully CCW and then CW. The output should switch to SPA heating when the SPA TEMP adjustment knob is rotated CW and to DHW heating when rotated fully CCW. Now with the SPA TEMP adjustment knob fully CW, rotate the DHW TEMP adjustment knob CW. The output should switch back to DHW heating. If all is well so far, great. Next switch the priority switch to SPA, rotate the DHW and SPA TEMP adjustment knobs fully CW. The SPA heating LED should be on. Now rotate the SPA TEMP adjustment knob CCW. The output should switch from SPA to DHW. Leaving the SPA TEMP adjustment knob fully CCW, rotate the DHW TEMP adjustment knob fully CCW. The DHW output LED should remain on. So there you are. At least the switching is working. You can check the turn ON and OFF differentials with your Quick-Check. If this checks out and you still have a problem, it's probably with the output relays, the output wiring, or maybe even a trace on the printed circuit board.

 

If I've made a mistake or have left out some important information or you otherwise take exception to what I have written, please write to me (c/o CoSEIA or to my address listed in the CoSEIA membership directory) and we will include your comments in the next newsletter.

 

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