pct88
Member
Given the particularly cold weather in recent days I decided I should automate the fresh Outside Air fan that warms outside air through a heat recovery ventilator unit, then into the return plenum of the furnace. I found that temperatures below 0 are low enough that the HRV is unable to preheat the OA enough to avoid a few minutes of particularly cool air as the furnace deals with the initial 30-40 degree air.
Yes, I have experimented with lowering the OA fan speed, (suggestions for a UPB Fan Speed control?) added insulation, turning off the fan entirely, etc... My concern is that due to the radon levels in the area we have two sub slab radon fans that continuously pull in outside air. The HRV warmed OA helps balance this, and also keep the radon levels down.
I have set up the following code that is intended to poll the thermostat to determine when the furnace is running, see if it is below 40 outside, wait two minutes (or more depending on when the heat turns on during the two minute polling period), double check that the furnace was not turned off again in the interim, then start up the OA fan. When the furnace cycles off the OA fan turns off immediately.
Does this code look like a reasonable way to provide this functionality? I realize there are always multiple ways to get the same results from programming- I would prefer not to discover that perhaps the OmniStats lock up if poled too often, or repeating the UPB on and off signals every two minutes will cause other issues and I should add code so that only a single on and off UPB update is sent per furnace cycle.
CODE
52. // OA Supply
53. EVERY 15 MINUTES
AND IF Outside Temp CURRENT READING IS LESS THAN 45 BY MORE THAN 5
THEN OA < 40 Deg. ON FOR 16 MINUTES
54. EVERY 2 MINUTES
AND IF Living Room SYSTEM STATUS IS HEATING
AND IF OA < 40 Deg. ON
THEN Wait 2 Min. ON FOR 2 MINUTES
55. WHEN Wait 2 Min. OFF
AND IF Living Room SYSTEM STATUS IS HEATING
THEN Outside Air Intake Fan U50 ON
56. // Turn off OA Fan immediately when call for heat turns off.
57. EVERY 2 MINUTES
AND IF Living Room SYSTEM STATUS IS NOT HEATING
THEN Outside Air Intake Fan U50 OFF
/CODE
Yes, I have experimented with lowering the OA fan speed, (suggestions for a UPB Fan Speed control?) added insulation, turning off the fan entirely, etc... My concern is that due to the radon levels in the area we have two sub slab radon fans that continuously pull in outside air. The HRV warmed OA helps balance this, and also keep the radon levels down.
I have set up the following code that is intended to poll the thermostat to determine when the furnace is running, see if it is below 40 outside, wait two minutes (or more depending on when the heat turns on during the two minute polling period), double check that the furnace was not turned off again in the interim, then start up the OA fan. When the furnace cycles off the OA fan turns off immediately.
Does this code look like a reasonable way to provide this functionality? I realize there are always multiple ways to get the same results from programming- I would prefer not to discover that perhaps the OmniStats lock up if poled too often, or repeating the UPB on and off signals every two minutes will cause other issues and I should add code so that only a single on and off UPB update is sent per furnace cycle.
CODE
52. // OA Supply
53. EVERY 15 MINUTES
AND IF Outside Temp CURRENT READING IS LESS THAN 45 BY MORE THAN 5
THEN OA < 40 Deg. ON FOR 16 MINUTES
54. EVERY 2 MINUTES
AND IF Living Room SYSTEM STATUS IS HEATING
AND IF OA < 40 Deg. ON
THEN Wait 2 Min. ON FOR 2 MINUTES
55. WHEN Wait 2 Min. OFF
AND IF Living Room SYSTEM STATUS IS HEATING
THEN Outside Air Intake Fan U50 ON
56. // Turn off OA Fan immediately when call for heat turns off.
57. EVERY 2 MINUTES
AND IF Living Room SYSTEM STATUS IS NOT HEATING
THEN Outside Air Intake Fan U50 OFF
/CODE