Outdoor reset

[nate379]

Tell me if this makes sense.

I have an outdoor reset I need to wire. The sensor is supposed to go outside to measure outdoor temp.

It would be MUCH easier for me to put the sensor in the attic instead. Would I expect to get an accurate outdoor temp in the attic? It's vented well and there is 18-20" of insulation on the top of the ceiling. (~R50)

 

[rickairmedic]

Nate I generally put the outdoor temperature sensor on the outside condensor unit down under the electrical box on the unit . I would say if you cant put it there the next best location would be under the eves on your house . You wont get an accurate reading in the attic . When the sun hits the roof it will warm up the attic compared to outside.

Rick

 

[nate379]

Outdoor reset is for a boiler. No A/C needed when summer highs might at the very worst hit 80*

I have a remote weather station, going to put the sensor up there and see what it reads compared to outside temps.

 

[rickairmedic]

LOL Nate I had forgoted you lived among the frozen tundra . I guess give it a shot and see what happens .


Rick

 

[sneezer41]

Problem is sun. when it is sunny, the attic will get warm and upset the heating curve.

It is that hard to drill a hole?

If it gives you trouble, you know you are going to end up doing it twice.....

 

[nate379]

Sure it's easy to drill a hole... to the attic.

 

[redsky49]

On a sunny day, especially with a dark-colored roof, you could easily have temperatures in the attic considerably higher than ambient - 30 to 40 degrees are not unheard of. While you could possibly work with this, I would not recommend such an installation.

As a general rule, I have always specified the location for OA sensor as a north wall or eave where there would be no impact from sunlight. Location should be representative (i.e., not next to the clothes dryer outlet, etc.).

Equally important is to scale the correct operation of the sensor. For example, using Anchorage (no climatic data is available for Palmer), a 99% design temperature is -9 degrees F. A reset schedule might read as follows:

Boiler shall fire to maintain (circulating loop? Modify to suit.) HW temperatures as described below:

At outside temperatures above 60 degrees F , as noted by OA sensor, system shall remain in enabled status. HW Pump shall de-energize and boiler burner shall not fire.

Upon drop in OA temperature below 60 degrees F, the HW Pump shall energize. Upon confirmation of flow (flow switch), Boiler shall fire to maintain HW (circ. loop) temperature of 140 degrees F as determined by (circ. loop) aquastat. Under no circumstance shall minimum operating temperatures exceed the safe limits of the boiler as determined by the boiler manufacturer.

Boiler firing shall modulate in a linear fashion such that the (circ. loop) HW temperature shall maintain 180 degrees F at 10 degrees F OA temperature.

All operating setpoints shall be user adjustable. Boiler operation shall be disabled unless flow is confirmed.

Something like this, modified to suit your particular needs, is recommended as a starting point. Be aware that any system will require a commissioning period and some "tweaking" for optimal operation. You are starting to get into the more complicated realm of temperature controls and they are generally not "optimised" right out of the box.

Be aware also that the the various control devices must communicate with each other so that a common operating voltage is very useful.

Getting even fancier, you could also include flue gas temperatures, time of day, etc. into your sequence of operation, as well as fuel usage for your operating cost summaries. Once you have a computer into the system, you can tweak to your heart's content.

Good luck with your project.

as always, offered only as opinion

 

[ajaynejr]

Mount the sensor to best get the outdoor air temperature, for example on the north side of the house and not in direct sunlight.

Typically there is one sensor that merely prevents any of the thermostats from calling for heat or that prevents the circulator pump in a FHW system from coming on, when the outdoor temperature is above a certain threshold.

Getting a little fancier, a second outdoor sensor together with a second aquastat (boiler temperature sensor) may be installed so at an outdorr temperature above a certain threshold the boiler temperature is maintained a little lower, say 160 degrees instead of 190. Supposedly this makes room temperatures a little more consistent on a mild day since the furnace is supplying not quite so strong heat for longer periods of time (longer duty cycle) versus full blast for shorter periods of time.

This can be installed for "a coupla' hundred dollars". There are more elaborate systems you buy as a package to manage your existing boiler, include the above named components, perhaps include a microprocessor, cost a coupla' thousand dollars, and IMHO offer very little more in terms of benefits or additional energy savings.

 

[nate379]

The thing is the boiler is on the west side of the house and to put the sensor on the north side I would need quite a bit of wire, around 50ft. I might be able to run the wire across the attic and come out on the north side, not sure. There is about 2 feet of blown in up there so not easy to walk around.

The controller I have is a Taco PC700 which plugs into a Taco SR504 EXP zone control. Burnham boiler that is a primary/secondary loop and heats the floors in the house and garage.

 

[danski0224]

Is the boiler in a basement?

 

[nate379]

No in my attached garage.