Navitron Renewable Energy and Sustainability Forum

SOLAR THERMAL => Solar Thermal Systems => Topic started by: Antman on December 22, 2006, 03:18:56 PM

Title: Solar Forum FAQ - Controls and electrical aspects
Post by: Antman on December 22, 2006, 03:18:56 PM
Welcome to the Solar Forum Control/Electrical FAQ

This section of the Solar Forum FAQ covers the Solar Controllers and electrical aspects of a solar installation.

For the Solar Forum Plumbing FAQ please see (

The FAQ has being split due to maximum post length being reached, thus preventing additions

It is intended to supplement the FAQ on the Navitron website see (  and is based on common questions and discussion threads within the Forum.

Please note: This topic is locked to prevent it becoming an eternal thread, as it is intended to be an FAQ only. It will be updated whenever suitable topics arise.

What are the differences between the solar controllers?
The Resol DeltaSol A is a basic solar controller with one output to control the solar pump and supplied with two sensors. Simple setup with adjustable DeltaT setting and selectable freeze-protection only.

The DeltaSol Ax adds adjustable maximum and minimum temperature operating limits and a manual operation switch (useful for setting up and testing).

The DeltaSol B/1 is a basic digital controller with one output to control the solar pump and is supplied with two sensors (for manifold and lower cylinder sense).

The DeltaSol BS/3 is a higher specification controller including:
-  an additional relay output to control the Heat Dump option should the system reach maximum temperature (e.g. when on holiday),
-  a Freeze Protection function (controller will prevent manifold from freezing by running solar pump when necessary if antifreeze is not used),
-  supplied with additional sensor to monitor the upper cylinder temperature,
-  an optional fourth sensor can be fitted to monitor Return pipe temperature.

The DeltaSol BS/4 is similar to the BS/3 but incorporates variable speed control on the solar pump output.

The DeltaSol BS/Pro controller has two relay outputs allowing either:
a) Heat dump control as per BS/3 model,
b) Independent pump control of East-West facing panels.

The DeltaSol ES can cope with East-West panels, Heat Dump with virtually any system you could want. Also has RS232 and VBus interfaces. Uses similar user-friendly programming as the BS/3 and BS/4.

The DeltaSol M does everything except tie your shoe laces - but you may spend as long programming it as installing the system itself  ::)

The new Navitron TDC3 has all the functionality of the Resol BS/4 with several additional functions including automatic Anti-Legionella protection. Additional parameters are used to program the functions and setpoint temperatures hence there are fewer direct equivalents of program parameters when compared to the Resol controllers in the table.

The table below attempts to compare and illustrate the major differences between the Resol range and Navitron TDC3 controllers together with the common control parameter names and values.
It should be noted that Resol products are under continuous development and parameter values can be subject to change between shipments.

Controller modelAAxB/1BS/3BS/4BS/ProESMTDC3
Digital displayNoNoYesYesYesYesYesYesYes
No. sensors possible22244410123
No. sensors supplied22233???2
No. relay outputs11122210122
Variable pump speedNoNoNoNoR1R1-2R1-3R1-4R1
Manual relay controlNoYesYesHNDHNDHNDHNDYesYes
Operation hours counterNoNoYesYesYesYesYesYes ?Yes
DeltaT on settingYesYesDODTODTODTODTOTon**
DeltaT on range+2 to 16K+2 to 16K+2 to 10K+1 to 20K+1 to 20K+1 to 20K+1 to 20K+1.5 to 20K0-99 degC
DeltaT off settingFixedFixedDFDTFDTFDTFDTFToff**
DeltaT off range1.6K1.6K+1 to 9K+0.5 to 19.5K+0.5 to 19.5K+0.5 to 19.5K+0.5 to 19.5K+1.0 to 19.5K4-20 degC
Freeze protectionYesYesNoOCF / CFROCF / CFROCF /CFROCF / CFRYesYes
- Freeze prot rangeFixed 4CFixed 4C - -10 to 10C-10 to 10C-10 to 10C-10 to 10CFixed 4C-25 to +10C
Collector abs max shutdownNoNoCLEMEMEMEMTcolnotYes**
Shutdown limit range 110-200C110-200C110-200C110-200C110-200C110-200C60-150C
Max Store tempNoPresetSXSMXSMXSMXSMXTspmaxYes**
- Max Store value range - 20 to 90C2 to 85C2 to 95C2 to 95C2 to 95C2 to 95C4 to 95C0-99C
Min Collector tempNoPresetCNOCN / CMNOCN / CMNOCN / CMNOCN / CMN ?TminS1
- Min Coll value range - 20 to 90C-10 to 90C-10 to 90C-10 to 90C-10 to 90C+10 to 90C ?0-99C
Dual East-West panelsNoNoNoNoNoYes1YesYesYes
Thermostat functionNoNoNoAHO / AHFAHO / AHFAHO / AHF1AHO / AHFYesYes
Heat Dump control range - - - 0 to 95C0 to 95C0 to 95C0 to 95C ? 0-99C
Heat Quantity Balancing 2NoNoNoYesYesYesYesYesYes
Re-cooling functionNoNoFN2ORECORECORECORECYesYes
Collector cooling function - - FN3OCX / CMXOCX / CMXOCX / CMXOCX / CMXTcolmax**
- Coll cooling range - - - 100 to 190 C100 to 190C100 to 190C100 to 190C80 to 160C60-150C
Language selectionN/AN/AEnEn/Ge/ItEn/Ge/ItEn/Ge/ItEn/GeEnEn
Controller modelAAxB/1BS/3BS/4BS/ProESMTDC3

Note 1: Not simultaneously
Note 2: With optional flowmeter(s)
Note **  The TDC3 controller uses additional programming parameters and is different to program from the Resol controllers

The temperature sensor cable is not long enough!
The Platinum Resistance Thermometer (PRT) temperature probes used are simple resistive devices. They can be readily extended using any twin flex or bell-wire. It is best to use screw-terminal blocks (choc-blocks) with the built-in wire protectors to prevent damage to the wires.

How hot will the water get?
Using a dedicated solar controller such as the Resol BS/3 allows accurate control of the water temperature circulating around the system and maximises the efficiency of the system.
The controller monitors the temperature difference between the panel manifold and the lower cylinder sensor.
The circulating pump is triggered when the difference exceeds the DTO setting (say 6 degrees)
The pump will stop once the difference drops below the DTF setting (say 4 degrees).

This means that if the cylinder (base) temp is 25C then the pump will start to run when the manifold temp reaches 31C.
As the water circulates and gives off its energy to the stored water the temperature in the cylinder will rise and the circulating water will drop.
Once the difference drops below 4 degrees then the pump will stop.

Therefore the actual cylinder temperature achieved will depend on the amount of solar radiation received by the panel on a given day and the volume of DHW used by the household in the meantime.

Do I need a Heat Dump?
OK - so this is the controversial one and has been the subject of much debate on the Forum - just put Heat Dump into the Search box.... ::)
The usual recommended cylinder temperature is 60-65 degrees C for a conventional DHW system. However a well designed solar system has the potential to exceed this during summer months - especially, and most importantly, when the householder is away for any length of time, e.g. on summer vacation.
If a solar system is designed so as to never exceed 65 deg C cylinder temperature under any circumstances (without a Heat Dump) then its performance will be marginal and it is unlikely to result in the expected fossil-free summer months of DHW production.

It has been confirmed that the Navitron supplied cylinders are guaranteed by the manufacturer to withstand and be functional to 95 degrees C. (Note: Do not assume that other manufacturers will automatically offer a similar guarantee!)
In theory[/i], this negates the need for a Heat Dump on a correctly sized system. However, anyone who installs a system that is 'permitted by design' to operate at elevated temperatures must install a Thermostatic Mixing Valve (TMV) on the outlet of the cylinder. This is essential to prevent a virtually guaranteed scalding injury that would result from skin contact with DHW at elevated temperatures. Anyone who doubts the wisdom of doing this should refer to the guide at ( . A professional installer should be aware that there would be little chance of a defence in court for scald injury claims resulting from an inadequately controlled solar system (since a competent installer should know that a well-designed solar system is potentially capable of producing dangerously high DHW temperatures under high insolation conditions.)

That said, you need to decide what temperature you are prepared to accept as stored water. Consider also that where the cylinder is permitted to operate at elevated temperatures, the solar loop will be DTO degrees hotter. This may have implications on long term reliability of components especially the pump.
It may well be that you prefer to dissipate the significantly excess thermal energy via another route such as a dedicated Heat Dump or existing CH radiator(s).

The maximum cylinder temperature can be set in the controller using the SMX setting (on BS/3) which could be reached on days where there is no water drawn off (the occupants are on holiday for example). Before this point, there is a need to reduce the temperature of the stored water - via a heat dump.
For the Heat Dump control functions to work (and be accessible from the keypad) the BS/3 System Mode must first be set to "Arr 2".

If you are running the Heat Dump using AHO and AHF parameters, SMX needs to be set to a value of at least AHO + DTO - this is to allow the solar loop to continue loading the cylinder/store whilst the Heat Dump is operating. AHO should ideally be 0.5 higher in value than AHF e.g. AHO= 68.0, AHF=67.5

How do I wire it all up?
The electrical wiring must conform to BS7671  IEE 17th Edition and Part P of the Building Regulations. If the Heat Dump is incorporated utilising the boiler coil with the boiler inhibited via a relay, it is essential that both boiler and solar systems are supplied from the same socket or DP switch-fused spur. This is to prevent electrical danger arising from only one 'half' of the linked system being isolated during maintenance work.
This method is easy to implement with boilers having a common-neutral connection between boiler and system pump. Many modern condensing boilers have complex control electronics with the system pump electronically controlled and fed direct from the boiler control PCB. Modification of most of these is not recommended! However the Alpha CDR and Remeha Avanta (heat only) models are known to be compatible and generic system schematics are available to suit.

Examples of a standardised set of wiring schematics for the common S-Plan, S-Plan+ and Y-Plan heating systems schemes and components can be downloaded in Excel format from: ( and include information on how to incorporate the Heat Dump.