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 25 - September/October, 1997

 

Programmable Differential Temperature Controllers©

 

This is the tenth and final 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 Solar Controls Corp. 80-171 (for DHW systems) and 77-176 (for air space heating), the Rho Sigma/Watsco RS121, the Solaron HC0115, and the TACO line of controllers. Both Solar Controls Corp. controllers use 30K ohm thermistor sensors. The Solaron HC0115 also uses 30K ohm thermistor sensors. The Rho Sigma requires 10K ohm sensors while the TACO line uses 3K ohm thermistors. None of these controllers has much in the line of programming, but still need to be mentioned, primarily for completeness for this series of articles.

 

The Solar Controls Corp. 80-171 (for DHW) has both high limit (boil protect) and low limit (freeze protect) circuitry that enables the controller to turn the output off at a storage sensor temperature of 180° ±5° F and provide recirculation freeze protection when the collector sensor drops to 40° ±5° F. Either or both circuits can be disabled by cutting the appropriately labeled diodes out of the circuit on the printed circuit board. Certainly in this part of the country, the freeze protect diode should be cut out. The Solar Air Mover (SAM) 77-176 (for air space heating) circuit board contains two jumpers, UP1 and UP2. With UP1 open (cut), the controller will turn off the SAM blower and shut the damper to the home when auxiliary heat is requested. Therefore the SAM blower will turn off when stage 1 heating (W1) is calling for heat and solar is not available or when stage 2 (W2) is calling for heat. With UP2 open (cut), the controller will stop the auxiliary fan voltage from appearing between terminals 14 and 15 under all conditions except a fan on condition from the thermostat. Other programmable features involve modifications to the temperature sensing limits. The controller is delivered with turn ON and turn OFF differentials of 45° and 25° F respectively. These temperature differentials can be changed by doing the following: (1) Instead of connecting the cold storage sensor to terminals 4 and 5, connect the sensor to terminals 3 and 5. (2) Connect a resistor, R1, between terminals 3 and 4. The resistor value can be chosen from the following table.

 

Differential ON ° F

Differential OFF ° F

Resistor, R1 - ohms

45

25

None

40

20

4,700

35

15

10,000

30

10

16,000

25

5

24,000

 

The controller compares the temperature of the collector sensor or the temperature of the hot storage sensor to the programmed delivery temperature (85° F) to determine if solar heat is available. The programmed delivery temperature can be changed by connecting a resistor, R2, to terminals 8 and 9 according to the following table.

 

Programmed delivery temperature, ° F

Resistor, R1 - ohms

85

None

90

200,000

100

60,400

110

32,400

120

21,000

130

14,700

 

The Rho Sigma/Watsco RS121 incorporates a field adjustable pot for high temperature cutoff. Its range is from 120° to 250° F.

 

The Solaron HC0115 has a Summer /Winter switch. In the Summer position, domestic water (if this option is used) will be preheated whenever enough solar energy is available to activate the system. When the stored water temperature reaches the set point of the Tw sensor (about 140° F) the system will shut down until the stored water temperature drops about 100° F. When the switch is in the Winter position, domestic water will be preheated anytime the system is storing heat or heating the house from the collector.

 

The TACO line of controllers is manufactured by Heliotrope. It therefore follows that TACO controller operations and options are similar. The following table lists these features.

 

Product Number

Sensors to be Ordered Separately

Sensors Included With Controller

Sensors to be Ordered Separately

Function A Off Below 80° F

Function B Freeze Recycle

Function C High Limit Off

T-60 Hardwired

None

Two each S-1

One each S-7

Two each S-5

One each S-1

T-80

External knob for adjustable "High Limit"

Three each S-1

One each S-7

Two each S-5

Included with controller

T-30

One 120V output for pump and one 120V output for drain dump valve

Two each S-1

Two each S-1 & two each S-6

Two each S-7

One each S-1

T-70 Line Cord & Receptacle

One receptacle for pump/fan

Two each S-1

One each S-7

Two each S-5

One each S-1

T-50

Two receptacles wired together

Two each S-1

One each S-7

Two each S-5

One each S-1

T-40

One receptacle for pump and one receptacle for drain dump valve

Two each S-1 & two each S-6

One each S-7

 

One each S-1

T-700 Line Cord & Receptacle with Digital Display

One receptacle for pump/fan

Two each S-1

One each S-7

Two each S-5

One each S-1

T-590

Two receptacles wired together

Two each S-1

One each S-7

Two each S-5

One each S-1

T-490

One receptacle for pump and one receptacle for drain dump valve

Two each S-1 & two each S-6

One each S-7

 

One each S-1

 

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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