Outdoor sensor

Harvey Ramer

I'm convinced the only reason we put outdoor sensors outside, is because it says outdoor on the box. 

I can't think of a logical reason the sensor shouldn't go in the air intake for direct vent appliances.  I mean; maybe WWSD, but that is useless 99% of the time and is only there because it doesn't cost anything extra. 

Discuss 

Jamie Hall

For a direct vent boiler, it could go in the intake vent. No particular reason not to, assuming the boiler or circulator control logic doesn't need an outside air parameter when the boiler is off (such as, perhaps, a mixing valve for a continuous circulation system). However, not all boilers are direct vent...

Harvey Ramer

Jamie Hall said:

For a direct vent boiler, it could go in the intake vent. No particular reason not to, assuming the boiler or circulator control logic doesn't need an outside air parameter when the boiler is off (such as, perhaps, a mixing valve for a continuous circulation system). However, not all boilers are direct vent...

Good point. Some scenarios would cause a problem in the off cycle with an active heat demand. However, manufacturers could easily overcome that with a few lines of code that does a setpoint lock during those periods. 

It just dawned on me the other day and so I tried it. It's working just fine so far. It just seems silly and irresponsible to install a sensor outside when you are bringing outside air within a few feet of the control that wants to know what temperature it is. 

Anybody installing DV appliances knows that getting the OSS in the right place can be a real PITA. Sometimes you have to get to the opposite side of a building with no good way to do it. 

I think for a few extra bucks a manufacturer could run with this and make it a hot 🔥 selling point. 

hot_rod

some heat could migrate up the intake also

Harvey Ramer

hot_rod said:

some heat could migrate up the intake also

True. But that would only happen/matter while the boiler was off with an active heat demand. A few lines of code to do a setpoint lock during that time would solve that problem.

ScottSecor

Not every air intake is located on the north facing wall of the building. 

ratio

The only reason the OAT sensor is supposed to go on the north side is to avoid solar radiation. Mounting it in the intake, presumably near/inside the unit, would mean perhaps a lot less wiring. I think it'd be susceptible to influences from inside the building (it'd run warm, anywhere from slightly to significantly) but I can't recall the last time I looked at a 'properly' mounted OAT sensor & not seen anything that would influence it.

@Harvey Ramer, great idea! I've got a picture in my mind now, looks like one of those chinesium sensors that you can get on eBay, stainless & threaded to screw into a hole.

hot_rod

Harvey Ramer said:

hot_rod said:

some heat could migrate up the intake also

True. But that would only happen/matter while the boiler was off with an active heat demand. A few lines of code to do a setpoint lock during that time would solve that problem.

So the boiler would need to stat to get the accurate temperature reading? But if it were reading warm for heat leaking up the intake, it may not ever start, thinking it were in WWSD

I guess it would be application specific. My intake is only 5' and horizontal on a south facing wall, probably not a good candidate.

pedmec

All it would take to mess that up is to have the air intake directly over an asphalt driveway. All that heat coming off the driveway from solar gain would definitely cause an incorrect reading. Its easy enough to run a low voltage 2 conductor anywhere you want and not have to beholden to my air intake. Its the easiest part of the job.

I think the mousetrap works fine

Tom_133

good topic, and some cool thoughts.

I recently had one of those challenging boiler installs where getting the wire to a north wall was a pain if not not possible. The NTI FTVN has the wifi setup and allows you to use ITEMP so it gets your location and uses the temperature based off that location. Not perfect, but no blinking outdoor sensor, and no wire hassles. I do agree, that a boiler manufacturer could pretty simply make a sensor on the intake side that could solve 30 seconds after firing, but as hot rod said, only IF it allows the boiler to fire.

Thanks Harvey for the exercise. I like thinking outside the box
Tom

ratio

There's a number of wireless sensors available now as well. I've got my eye on https://hbxcontrols.com/wav-0110.php, but it's a little expensive to get one just to fool around with.

Voyager

Installed a concentric vent on my boiler. The intake air temp will be closer to the average temp between the outside air and the exhaust air temp. Probably can be accommodated by tuning the reset values, but for me installing the sensor wasn’t a big deal in my workshop, but in many homes things aren’t so simple.

I am sure the obstacles can be largely overcome with software, but there may always be some conditions that are hard to accommodate in software and the performance of the outdoor reset may be compromised. And often software “fixes” like this come with unintended consequences.

unclejohn

This reminds me of a discussion we had at ABC School. Can you locate the bulb for a expansion valve at the compressor? In the case of the ODS it seems that running the blower or inducer fan for 45 seconds or so before ignition would be enough to overcome most false reading from heat sources.

Lance

I like to think. Let us say I have a sensor labeled indoor. Is it ok to put outside? I think not. Non the less, outdoor means to monitor outdoor temps, further instructions may indicate to avoid false heat and cooling effects. False means not the same as true. What do we want true, false or maybe? Many controls are designed to a certain set of algorithmic logic approaches, some customizable. Freezing temps may create a start cycle to help prevent freeze damage, such as circulator pump, or low temp maintaining even if indoor stat is satisfied. I know a client who kept his boiler off while using a fireplace to save money. Let's just say two weeks of work repairing freeze splits in the basement didn't work well. AN outdoor stat control would have prevented it. Another reason to save money buying insurance. If it says "outdoor" and I put it "indoor" and I have to explain why, well, I don't see a customer logically understanding this. And when I say to someone you need to check the outdoor sensor, where are you going to look?

pedmec

I have the air intake temperature probe for my testo combustion analyser and have found that the temperature of the combustion air is never the same as the outside air when testing direct vent furnaces and boilers. whether its warm pvc (cpvc) from warm basement or friction of the pipe walls its definitely never read the same as outdoors.

But to be fair i didn't wait for extended period of time as i'm there for maintenance and safety testing. Also the probe are close to the boiler for accurate temperature measurement into the boiler. I will try to test when i go to another PM and drill close to the outside wall and experiment.

Another thought that came to me is what would happen in a warm basement and the vent material warmed up the air intake and OAT sensor during standby to the point that it might get warmer than the WWSD setpoint on the mild days.

Voyager

Lance said:

I like to think. Let us say I have a sensor labeled indoor. Is it ok to put outside? I think not. Non the less, outdoor means to monitor outdoor temps, further instructions may indicate to avoid false heat and cooling effects. False means not the same as true. What do we want true, false or maybe? Many controls are designed to a certain set of algorithmic logic approaches, some customizable. Freezing temps may create a start cycle to help prevent freeze damage, such as circulator pump, or low temp maintaining even if indoor stat is satisfied. I know a client who kept his boiler off while using a fireplace to save money. Let's just say two weeks of work repairing freeze splits in the basement didn't work well. AN outdoor stat control would have prevented it. Another reason to save money buying insurance. If it says "outdoor" and I put it "indoor" and I have to explain why, well, I don't see a customer logically understanding this. And when I say to someone you need to check the outdoor sensor, where are you going to look?

It should not be hard to change the name to intake air temp sensor and avoid confusion.

Dave Carpentier

Some units use wifi onto the internet to get current/forecast temperatures.
Do they make 'wireless' ODR boxes to avoid running wires (but then you have battery issues, I guess).

I can agree with the hassle of running a proper ODR wire, and trying to find alternatives.
Mine will require 75 ft or so to get to the north wall.

Harvey Ramer

Interesting conversation. As is true with all ideas in heating, one solution never addresses every circumstance.

However, this one is working. I know this because I haven't gotten any complaints about not enough heat. It's also particularly easy to do.

kcopp

Tekmar 087 is wireless and lets you use a variety of sensor settings...10K (type 2 and 3), 5K, 12K and 20K resistance setting options .

BobZmuda

Honestly I’m not seeing a compelling reason to not try this. Freeze protection perhaps, but in most cases that won’t be an issue if the boiler is the main source of heat and if it turns on or off based purely on what the thermostat calling for heat. 

So the water temp is lower for a while on startup?  That’s likely a good thing.  More efficient operation, less radiator noise, longer run time per cycle.  I might try this at my house to test it out.  

Of course I’ll have to disable the setting that turns off heating mode when the outdoor temp is too high. The other issue might be with how a boiler reacts to large changes in the “outdoor” air temperature in a short time frame. 

Doug_7

I have a different philosophy. I provide a hard-wired "Solar Compensated" outdoor temperature sensor for boiler outdoor temperature reset.

This sensor is installed on the roof inside a white PVC pipe, mounted vertically in clear air fully exposed to the sun. This "Solar Compensated" outdoor temperature will read a few degrees higher than the temperature in the shade when the sun is shining, the same when it is cloudy, and a few degrees cooler at night when there is dark-sky radiation.

This "Solar Compensated" outdoor temperature sensor more closely follows the actual outdoor temperature and heat losses that the building is experiencing. Outdoor temperature reset will be lower when the sun is shining and higher at night when dark-sky radiation becomes an additional heat load.

I think this is a smarter way to use outdoor temperature reset, which will produce energy savings over the course of a year. Just a different way to think about boiler water temperature control.

Dave Carpentier

Is this "Solar Compensated" unit sealed ? If it has a reasonably small volume, would the solar gain on it, especially on a windless day, not heat up the air inside ? I think the small vol would heat much more rapidly than the counterpart of the house.
Also, what about partially cloudy days where its sunny for a bit then cloudy, then sunny etc. The target temp would be hunting around ?
The idea of incorporating solar effect is certainly valid though.

How about a shade-side "traditional" ODR thermal sensor but then adding a light sensor to bias the resistance a bit ? Best of both worlds ?

Doug_7

The sensors are enclosed in a 4" diameter white PVC pipe about 18" long, mounted vertically, with a 4" white PVC cap on top, sealed with silicone grease. It is full of air and has 3 Thermistors inside. Intentionally large to provide a more stable temperature.

This shape gives the same exposure to the sun at any time of the day. The temperature does not cycle noticeably with passing clouds. Will be several degrees warmer when sunny and several degrees cooler at night than a conventional sensor in the shade.

The building feels the effect of the sun shining or of dark-sky radiation quite quickly over a very large surface area. This "Solar Compensated" sensor responds a bit more quickly to give you a preview of what is coming.

I have used this "Solar Compensated" outdoor temperature sensor for about 20 years to provide "Solar Compensated" outdoor temperature inputs for the boilers and chiller in a commercial building. It just seems logical to me that the sensor should know if it is sunny or dark outside.

Works great.