What are the advantages of an outside temp sensor on boiler?

[blondini]

I fitted an external WC sensor to my Biasi M110 combi.
I couldn't locate a Biasi sensor and rang Biasi technical who at first told me Biasi's didn't support this feature and asked why I wanted to use it. They then said weather compensation is only of use in countries like Sweden.
Later I noticed in the manual that the resistance curve for the weather comp sensor was the same as the heat exchanger NTC's on the Biasi so used one of them. (Cheap)
So far it is working well. I chose a fairly steep compensation curve due to having an old house with poorly insulated solid walls. With an outside temp of 15 degC the boiler sends water to the rads at about 30 degC but with an outside temp of 5 degC it sends the water out at about 60 degC.

Dave

Excellent tip! Thanks for the info.

I couldn't locate one either. Biasi told me they didn't supply the external temp sensor in the UK because it wasn't needed in our climate. I wasn't convinced about that logic and now that I'm having to nudge up the boiler temp as the weather gets colder I know I was right. Now how about an indoor sensor that works the other way? Can it be done??

 

[NGBod]

NTC's What does this mean? A clamp-on temp sensor? If so, you one of these outside in a box?

It's just a screw in, stainless steel bodied, temp sensor about 14mm dia and 20mm long. I soldered 3amp flex to the spades and insulated them with heatshrink. The flex is fed through a hole in a northerly facing wall in a place not in direct sunlight and the sensor body is secured in the hole with silicon so the tip is protruding. A hood screwed and sealed against the wall over the sensor keeps it dry to prevent evaporation affecting the readings.

Dave

 

[NGBod]

I couldn't locate one either. Biasi told me they didn't supply the external temp sensor in the UK because it wasn't needed in our climate. I wasn't convinced about that logic and now that I'm having to nudge up the boiler temp as the weather gets colder I know I was right. Now how about an indoor sensor that works the other way? Can it be done??

For the Biasi I later found the Honeywell WC sensor has the same resistance curve but the cost is more.
The user selectable weather compensation curves in the Biasi all have a positive gradient so you would need to find a PTC with the same resistance curve (reversed) to use indoors. I think you will run into problems as it's not designed to work on indoor temps. Also whats the point when the outside temp comp works so well.

Dave

 

[blondini]

Now how about an indoor sensor that works the other way? Can it be done??

For the Biasi I later found the Honeywell WC sensor has the same resistance curve but the cost is more.
The user selectable weather compensation curves in the Biasi all have a positive gradient so you would need to find a PTC with the same resistance curve (reversed) to use indoors. I think you will run into problems as it's not designed to work on indoor temps. Also whats the point when the outside temp comp works so well.

Dave

I didnt word that very well, I was in a rush. I will certainly copy and use 'your' excellent outside temp sensor iarrangement thanks. Was just mulling the possibility of further refinement.

 

[Doctor Drivel]

NTC's What does this mean? A clamp-on temp sensor? If so, you one of these outside in a box?

It's just a screw in, stainless steel bodied, temp sensor about 14mm dia and 20mm long. I soldered 3amp flex to the spades and insulated them with heatshrink. The flex is fed through a hole in a northerly facing wall in a place not in direct sunlight and the sensor body is secured in the hole with silicon so the tip is protruding. A hood screwed and sealed against the wall over the sensor keeps it dry to prevent evaporation affecting the readings.

Dave

The soldering may affect the sensor. Should be a weatherproof box just laying on the bottom with spade or screw connections. Easy to replace then.

 

[Doctor Drivel]

I couldn't locate one either. Biasi told me they didn't supply the external temp sensor in the UK because it wasn't needed in our climate. I wasn't convinced about that logic and now that I'm having to nudge up the boiler temp as the weather gets colder I know I was right. Now how about an indoor sensor that works the other way? Can it be done??

For the Biasi I later found the Honeywell WC sensor has the same resistance curve but the cost is more.
The user selectable weather compensation curves in the Biasi all have a positive gradient so you would need to find a PTC with the same resistance curve (reversed) to use indoors. I think you will run into problems as it's not designed to work on indoor temps. Also whats the point when the outside temp comp works so well.

Dave

You can put the outside weather sensor in the room. This is direct modulation of the burner by the room temp. You need to select the correct control curve for it to work right. Usually a very narrow one.

 

[NGBod]

For the Biasi I later found the Honeywell WC sensor has the same resistance curve but the cost is more.
The user selectable weather compensation curves in the Biasi all have a positive gradient so you would need to find a PTC with the same resistance curve (reversed) to use indoors. I think you will run into problems as it's not designed to work on indoor temps. Also whats the point when the outside temp comp works so well.

Dave

You can put the outside weather sensor in the room. This is direct modulation of the burner by the room temp. You need to select the correct control curve for it to work right. Usually a very narrow one.

Yes of course it will work inside without reversing the compensation, thanks for correcting me. External compensation will still give more stable temps with less cycling of the boiler.

 

[Rog200455]

After reading the replies I now want to add the external sensor. The Ultracom wiring diagram shows where to connect it, however I suspect that there is some setting up to do? I am now familiar with the first level diagnostic menu, however there is a second level menu which is password protected. Am I correct in assuming that I have to get to this menu to set up the external sensor?

 

[Doctor Drivel]

Later I noticed in the manual that the resistance curve for the weather comp sensor was the same as the heat exchanger NTC's on the Biasi so used one of them. (Cheap)
So far it is working well.

Did you have the data sheets for these components? This is not the sort of info in the service manuals.

 

[Onetap]

NTC's What does this mean? A clamp-on temp sensor? If so, you one of these outside in a box?

It's just a screw in, stainless steel bodied, temp sensor about 14mm dia and 20mm long. I soldered 3amp flex to the spades and insulated them with heatshrink. The flex is fed through a hole in a northerly facing wall in a place not in direct sunlight and the sensor body is secured in the hole with silicon so the tip is protruding. A hood screwed and sealed against the wall over the sensor keeps it dry to prevent evaporation affecting the readings.

Dave

The soldering may affect the sensor. Should be a weatherproof box just laying on the bottom with spade or screw connections. Easy to replace then.

Try http://www.sontay.com/.

They sell thermistor temperature sensors to match the common BMS systems (Honeywell, Trend, Johnson, TAC, etc). You'd have to match the temperature/resistance with the Biasi thermistor. They sell the sensor in various packages (immersion, wall-mounted internal, external, duct, etc.) It's easier than trying to assemble a thermistor into a weather-proof enclosure. The Trend-type (10k ohms at 21 degC, ISTR) is fairly common.

It's also very important that the outdoor sensor is on a north wall, where the sun won't shine on it and where the bathroom extract fan doesn't blow hot air on it (seen it). It's meant to measure air temperature and heat gains from solar radiation will cause a huge error. Ever put your hand on a dark car roof on a sunny day? Same effect.

 

[Rog200455]

After reading the replies I now want to add the external sensor. The Ultracom wiring diagram shows where to connect it, however I suspect that there is some setting up to do? I am now familiar with the first level diagnostic menu, however there is a second level menu which is password protected. Am I correct in assuming that I have to get to this menu to set up the external sensor?

I have now received the setting up info from Glow Worm tech support, via e-mail. Very impressed with the service.

 

[Doctor Drivel]

I fitted an external WC sensor to my Biasi M110 combi.

Does it have room temperature influence, using a temperature sensor rather than a simple on-off stat.

 

[NGBod]

Later I noticed in the manual that the resistance curve for the weather comp sensor was the same as the heat exchanger NTC's on the Biasi so used one of them. (Cheap)
So far it is working well.

Did you have the data sheets for these components? This is not the sort of info in the service manuals.

The Biasi service (or installation manual?) has resistance v temp graphs for the two sensors and both graphs are the same.

 

[NGBod]

I fitted an external WC sensor to my Biasi M110 combi.

Does it have room temperature influence, using a temperature sensor rather than a simple on-off stat.

No, it has several different compensation curves where x/y = outside temp/ CH temp. You select a curve during programming and then the boiler follows that.

 

[Agile]

One of the best features of the Biasi M110 is that it has weather compensation!

It has to be enabled according to the instructions and the curve chosen.

I am working on a design for combined internal/external sensors.

For anyone to say its not required in the UK was rather stupid!

Tony