Differential temperature Controller

Review of Differential Temperature Controller for Solar Hot water System


Solar hot water system needs a temperature controller to control pump(s) operation based on collector and tank different temperature, Current market available types are as follow:

1. Goldline Serial

Goldline GL-30 differential control is designed to provide maximum operating efficiency and flexibility. It is capable of handling most differential temperature control functions for space or water heating.

The GL-30 output is designed to operate a circulator or fan when sensing an appropriate temperature differential. Adjustable differential, from 8° to 24°F, allows the GL-30 to be tailored to specific needs of the system. Storage high limit, adjustable from 110° to 230°F, protects most solar storage systems. Recirculation capable and numerous other options available. Relay rated at 10 amps output.

$140 (www.siliconsolar.com)

2. AECA serial

The Steca model TR0301U differential temperature control provides for the automatic, safe, and reliable operation of domestic solar water heating systems. The control output is wired to a pump that circulates the heat transfer fluid between the solar thermal collectors and the storage tank during the course of the day. This microprocessor-based control utilizes two RTD type sensors to monitor collector and tank temperatures with digital accuracy.

The LCD gives the homeowner a variety of real time information including system temperatures at up to three separate locations. The consistent use of simple pictograms ensures ease of operation and troubleshooting. In addition to the primary function of turning the circulating pump on and off during the day, the TR0301U provides important diagnostic and safety functions. For example, the LCD pictograms will indicate fault conditions such as sensor shorts or pump failure. The installation manual also clearly describes the fault symptoms, possible causes and remedies.

The control features a total of three inputs and one 120 VAC output for the circulating pump. The load side is fuse protected. The control package includes two RTD type (resistance temperature detector) sensors, a seven foot line cord and a spare fuse. An optional third sensor displays the upper tank temperature and eliminates the need for an analog thermometer and fittings.

The numerous additional features of the TR0301U include an adjustable on/off differential (8 - 20° F) and high limit (32° F - 205° F), an evacuated tube collector function, vacation overheat protection to minimize collector stagnation, and a freeze-recirculation option. Temperatures can be displayed in either Fahrenheit (F°) or Celsius (C°).

FEATURES:

1. Digital Accuracy
2. LCD Provides Real Time Operating Temperatures At Up To Three Locations
3. Animated Representation of System Operation
4. Sophisticated Monitoring and Fault Diagnostics
5. Fused Output Protection For Pump Circuit
6. Varistor High Voltage Spike Protection
7. RTD Type 1000W Sensors
8. Adjustable On/Off Differential and High Limit
9. Evacuated Tube & Freeze Recirculation Functions
10. Vacation Overheat Protection
11. Accessible Side-Mounted On, Off, Auto Switch
12. Three Temperature Sensor Inputs/One 120 VAC Output

$145 (www.sunearth.com)

3. AIBC serial

This AIBC-868 differential temperature controller is pretty functional, the display unit has a blue background LCD display and displays when the electrical element is operating, when the pump is running and when freeze protection is in operation.

The controller comes with its own operating manual, and this is a supplement to make it easier to program for north America.

MAIN Functions

1. Clock – 24 hour time display
2. Water temperature – The display shows the temperature in the tank (geyser) and at the solar collector panel.
3. Solar circulation pump – temperature difference controlled.

3.1 When the temperature difference between the collector (hotter) and the tank (cooler) exceeds the switch-on temperature, the pump is started. This transfers hotter water from the collector panel to the tank. The temperature difference is adjustable from 2 deg C to 15 deg C. The default value is 10 deg C.

3.2 When the temperature difference between the collector (hotter) and the tank (cooler) drops below the switch-off temperature, the pump is stopped. The temperature difference is adjustable from 0 deg C to 10 deg C. The default value is 5 deg C.

4. Electrical element timing. The electrical booster can be set to run 3 times in a 24 hour period. If the tank temperature (T1) is 5 deg C less than the set temperature, the electrical element switches on until the set temperature is reached.
5. Hot water circulation pump – This is used in large installations where there is a long hot water supply loop. This pump circulates hot water through the complete system. It runs for 3 minutes, then stops for 15 minutes. It can be programmed to run 3 times during the day.
6. Instant circulation. It is possible to start the pump at any time. It will run for 3 minutes, then stop automatically
7. Freeze protection. The controller has freeze protection which prevents damage to the collector panel and piping. When the temperature in the collector panel drops to a set temperature, the circulation pump will start. It will run until the temperature is 5 deg higher than the set temperature. This temperature can be set from 2 deg C to 15 deg C. If the tank temperature is lower than the switch-on freeze protection temperature after the pump has started, then the electrical element will switch on until the switch off freeze protect temperature is reached.

$136 with free shipping (www.aibcusa.com)

4.Delta Serial

DTT-94 Differential Temperature Controller with line chord

two 10K sensors to perform all temperature sensing functions. Its basic function is to monitor collector and storage temperatures, and to operate a circulating pump or blower at the appropriate temperature differential. Can also provide freeze protection by recirculation, storage tank high limit and positive off when the collector temperature is below 80°F. Line cord with one receptacle. Field selectable differential 18°/5° or 9°/4°; 10 amp rated relay. UL listed.

This controller is the same as the DTT-84 only with a power line chord.

$147 (www.solardirect.com)

Conclusion:

As a basic control system, all four controllers works fine, however, as Delta and Goldline have no LED display and less options of functional, they are out of date products. AECA and AIBC serials are quite decent. The clock function of AIBC serial allows user to easily monitor and record solar system performance.