Thermostat with adjustable cycle rate

[Archery1]

How long the system stays off once the stat is satisfied is a function of heat gain within the home. How long it takes to cool the home off once the system stat calls for cooling is a function of unit size. Thermostats are simply switches that automatically turn the system on and off depending on the temperature it senses.

You do bring up an interesting point to consider concerning heat gain and time elapsed. Yes, they do make thermostats with 3-degree variance, or adjustable to 3-degrees, but from what you point out, it isn't about that anyway. Plus, you then have to feel the temp swings more.

Heat gain being the function of the home design, it's going to gain the same amount no matter the change up on time a/c running. So it runs longer per period? Might be better on unit with longer cycling. But, for RH, seems total run time over 24 hours is a matter of heat gain v. heat removal (unit size and function) so total day's run time will be almost unchanged. Trying to learn a new zoned system myself with Aprilaire fresh air settings and RH settings. Still can't figure out why fan runs almost constantly some days and not so others no matter RH setting?

[03Lightningrocks]

How long the system stays off once the stat is satisfied is a function of heat gain within the home. How long it takes to cool the home off once the system stat calls for cooling is a function of unit size. Thermostats are simply switches that automatically turn the system on and off depending on the temperature it senses.

You do bring up an interesting point to consider concerning heat gain and time elapsed. Yes, they do make thermostats with 3-degree variance, or adjustable to 3-degrees, but from what you point out, it isn't about that anyway. Plus, you then have to feel the temp swings more.

Heat gain being the function of the home design, it's going to gain the same amount no matter the change up on time a/c running. So it runs longer per period? Might be better on unit with longer cycling. But, for RH, seems total run time over 24 hours is a matter of heat gain v. heat removal (unit size and function) so total day's run time will be almost unchanged. Trying to learn a new zoned system myself with Aprilaire fresh air settings and RH settings. Still can't figure out why fan runs almost constantly some days and not so others no matter RH setting?

The air conditioning system has two jobs. Remove heat from inside the home and dehumidify the air. It will only dehumidify while it is running.Relative humidity settings are tied into the blower speed. The theory being that by slowing down how fast the air moves across the evaporator coil, it allows the coil to remove more humidity from the air. The catch to this theory is that the air also must move fast enough to keep the coil from freezing up. Variable speed and two speed outdoor units, when installed with variable speed indoor blowers, have been a big help in achieving this balance. If your humidistats are set up to actually call for the outdoor unit to run to bring humidity down, this would explain why the air is constantly blowing. If the air is blowing but the outdoor unit is not running, it will actually increase humidity in the home. I would recommend a setting for the humidity at no lower than 40%-45%. Any lower than that and it will likely run all the time. It is real hard in DFW and Houston to get the humidity in the home lower than that anyway.

Oh... on the fresh air settings. If it were me, I would shut them down to near no fresh air in the summer months. The high heat outside is fighting your humidity removal. During the winter, crank them wide open.

[strogg]

Thanks everyone for your input so far. I've learned a lot despite my brain being over capacity as it was.

I took the temperatures of the supply and return grills with my trusty IR thermometer when the AC was operating. It was an 17-18 degree delta at its coolest (54 and 72 degrees). The filters are still clean, the outdoor units were also clean, and the coils were clean the last time they were checked a few months back. I can check in the morning when it's not so hot in the attic.

I also noticed something stupid that I can't believe I didn't piece together for the past 3.5 years I've lived here. As I was adjusting the downstairs t-stat again, I felt a breeze on my hand... The thermostat is about 6 feet diagonally from a supply duct. A little bit of cold air was blowing right at it. I'm going to move the thermostat to the other side of the wall in the morning. That side has pretty stagnant air and is also more representative of the actual temperature of the zone. The upstairs one is also 6 feet diagonally from the register, but I placed a barrier in between the two a year and a half ago, so that's no longer a real problem.

[strogg]

Oh... on the fresh air settings. If it were me, I would shut them down to near no fresh air in the summer months. The high heat outside is fighting your humidity removal. During the winter, crank them wide open.

What's your recommended intervals for fresh air ventilation throughout the year? I have a fresh air ventilation controller on each air handler, and I have a feeling the preset schedule is a bit too much.

[03Lightningrocks]

Oh... on the fresh air settings. If it were me, I would shut them down to near no fresh air in the summer months. The high heat outside is fighting your humidity removal. During the winter, crank them wide open.

What's your recommended intervals for fresh air ventilation throughout the year? I have a fresh air ventilation controller on each air handler, and I have a feeling the preset schedule is a bit too much.

I am not sure what options you have on your type controllers but I would set them up for minimal ventilation during the season it is 85 and above outside.

[Jusme]

Thanks everyone for your input so far. I've learned a lot despite my brain being over capacity as it was.

I took the temperatures of the supply and return grills with my trusty IR thermometer when the AC was operating. It was an 17-18 degree delta at its coolest (54 and 72 degrees). The filters are still clean, the outdoor units were also clean, and the coils were clean the last time they were checked a few months back. I can check in the morning when it's not so hot in the attic.

I also noticed something stupid that I can't believe I didn't piece together for the past 3.5 years I've lived here. As I was adjusting the downstairs t-stat again, I felt a breeze on my hand... The thermostat is about 6 feet diagonally from a supply duct. A little bit of cold air was blowing right at it. I'm going to move the thermostat to the other side of the wall in the morning. That side has pretty stagnant air and is also more representative of the actual temperature of the zone. The upstairs one is also 6 feet diagonally from the register, but I placed a barrier in between the two a year and a half ago, so that's no longer a real problem.

This may be a big part of your issue. At one facility I worked I could not get consistent heating/ cooling from one unit. I had three different HVAC techs out and they were unable to solve the problem. I decided the t-stat was not accurately reading temps and went to replace it. Whoever had installed it had cut a huge hole in the wall, so it was sucking air into the back of the t-stat. Hot in the summer and cold in the winter. I filled the hole with insulation, and voila, problem solved. Good luck.

[strogg]

Oh... on the fresh air settings. If it were me, I would shut them down to near no fresh air in the summer months. The high heat outside is fighting your humidity removal. During the winter, crank them wide open.

What's your recommended intervals for fresh air ventilation throughout the year? I have a fresh air ventilation controller on each air handler, and I have a feeling the preset schedule is a bit too much.

I am not sure what options you have on your type controllers but I would set them up for minimal ventilation during the season it is 85 and above outside.

The unit looks like it does the ventilation math on its own based on number of bedrooms, sq ftage, and blower cfm. I decreased the number of bedrooms, so it shouldn't run as often for now. I think sometime in the next few months I'll replace both ventilation units with a standalone ERV. That should hopefully help stabilize the indoor climate. It doesn't look all that hard to install, so I'll probably end up doing it myself.

[Archery1]

Oh... on the fresh air settings. If it were me, I would shut them down to near no fresh air in the summer months. The high heat outside is fighting your humidity removal. During the winter, crank them wide open.

What's your recommended intervals for fresh air ventilation throughout the year? I have a fresh air ventilation controller on each air handler, and I have a feeling the preset schedule is a bit too much.

I am not sure what options you have on your type controllers but I would set them up for minimal ventilation during the season it is 85 and above outside.

The unit looks like it does the ventilation math on its own based on number of bedrooms, sq ftage, and blower cfm. I decreased the number of bedrooms, so it shouldn't run as often for now. I think sometime in the next few months I'll replace both ventilation units with a standalone ERV. That should hopefully help stabilize the indoor climate. It doesn't look all that hard to install, so I'll probably end up doing it myself.

What system do you have? I know the Aprilaire controller will not allow operation if outside air temp is high. In a perfect world where all this stuff works as advertised, it should never allow the indoor humidity above the set amount no matter the controller settings.

[strogg]

What system do you have? I know the Aprilaire controller will not allow operation if outside air temp is high. In a perfect world where all this stuff works as advertised, it should never allow the indoor humidity above the set amount no matter the controller settings.

They are Honeywells of some sort. They use the W8150 controllers. They'll run regardless of what the climate is like outdoors. Seriously. My upstairs hygrometer reported 65% RH about an hour ago after the unit switched on without AC...

[03Lightningrocks]

What system do you have? I know the Aprilaire controller will not allow operation if outside air temp is high. In a perfect world where all this stuff works as advertised, it should never allow the indoor humidity above the set amount no matter the controller settings.

They are Honeywells of some sort. They use the W8150 controllers. They'll run regardless of what the climate is like outdoors. Seriously. My upstairs hygrometer reported 65% RH about an hour ago after the unit switched on without AC...

That is definitely what is causing your humidity problems. There are several methods for making that system draw in less air and run for less time. The best way to help you is to give you this link to the instruction sheet and trouble shooting chart for this controller/makeup air system. Personally, my goal would be to get it to run as little as possible. Regardless of what ASHRAE 62.2-2003 standards recommend. Reducing the run time on the blower assembly is far more important than amount of fresh air is added to system. What good is fresh air if it is creating 65% RH in the home? Here is the link. i hope it helps. https://forwardthinking.honeywellhome.c ... 8_0282.pdf

There is a way to reduce how much the damper is open in the device. The problem is bigger than just that. If this controller is calling for the blower while the AC is off, that air circulating through the ducts in your hot attic is just pumping heat into your home.

[LTUME1978]

An inexpensive and easy solution is to get a dehumidifier. Cost a couple of hundred bucks and should do the trick. I have used one for years. Helps to keep the humidity down without keeping the temperature too low in the house. Also helps in the humid times of the year when it is not that hot and the A/C does not have to run very much.

[03Lightningrocks]

An inexpensive and easy solution is to get a dehumidifier. Cost a couple of hundred bucks and should do the trick. I have used one for years. Helps to keep the humidity down without keeping the temperature too low in the house. Also helps in the humid times of the year when it is not that hot and the A/C does not have to run very much.

By coincidence, his make up air system has an option to install dehumidifiers with them. If I am understanding him correctly, his blower on his unit is running any time the make up air determines fresh air should be introduced to his home. Any time the blower in an attic is running, it is circulating air through ducts that are located in an attic that may be as hot as 125-140 degrees in the hottest part of the day. The longer the air is circulated through those ducts,the more the heat from the attic is absorbed. The ducts act as a heat exchanger and will move heat into the home which will increase humidity far beyond anything a dehumidifier will take out. The humidity in his home is not from humidity outside alone. It is being created by the luke warm air being circulated through his 76-78 degree house.

[Medley86]

We have some pro1 855 stats at the school I work for and they have all kind of settings, not sure offhand if there is a minimum cycle time. I know there are cycle limits built into it though.

We also had all units replaced on 2 campuses a couple years ago and several rooms have constant humidity problems. They have CO2 monitors controlling fresh air intake, the rooms that have problems have 3 tons on a single room so they don't stay on for long enough. Adding humid air makes it an unwinnable battle. Adjusted the dampers to open much less and it helped, didn't solve it but it took it from 75-80% to 60% humidity being the norm.

[strogg]

An inexpensive and easy solution is to get a dehumidifier. Cost a couple of hundred bucks and should do the trick. I have used one for years. Helps to keep the humidity down without keeping the temperature too low in the house. Also helps in the humid times of the year when it is not that hot and the A/C does not have to run very much.

By coincidence, his make up air system has an option to install dehumidifiers with them. If I am understanding him correctly, his blower on his unit is running any time the make up air determines fresh air should be introduced to his home. Any time the blower in an attic is running, it is circulating air through ducts that are located in an attic that may be as hot as 125-140 degrees in the hottest part of the day. The longer the air is circulated through those ducts,the more the heat from the attic is absorbed. The ducts act as a heat exchanger and will move heat into the home which will increase humidity far beyond anything a dehumidifier will take out. The humidity in his home is not from humidity outside alone. It is being created by the luke warm air being circulated through his 76-78 degree house.

You're spot on, 03Lightningrocks. The fresh air controller opens the damper, then turns on the blower w/o manually energizing the coils to circulate air. If the AC or reverse pump heat happens to be running, then lucky me. Otherwise, not so much. Based on the ASHRAE math, the dampers open for 13.5 and 16.5 minutes per hour for each zone before I messed with the schedule.

I was just thinking of something in the shower. What if I disable the schedules and rig the units to open up the fresh air damper to 1/3rd every time the air handler blower turns on via the thermostat, then have the damper close back up when the blower turns off? That would ensure a very small mix of fresh air with recirc air every time the AC/heater turns on. Would that solve the problem? Or would getting rid of the fresh air units and going for a standalone ERV be a better solution?

[03Lightningrocks]

An inexpensive and easy solution is to get a dehumidifier. Cost a couple of hundred bucks and should do the trick. I have used one for years. Helps to keep the humidity down without keeping the temperature too low in the house. Also helps in the humid times of the year when it is not that hot and the A/C does not have to run very much.

By coincidence, his make up air system has an option to install dehumidifiers with them. If I am understanding him correctly, his blower on his unit is running any time the make up air determines fresh air should be introduced to his home. Any time the blower in an attic is running, it is circulating air through ducts that are located in an attic that may be as hot as 125-140 degrees in the hottest part of the day. The longer the air is circulated through those ducts,the more the heat from the attic is absorbed. The ducts act as a heat exchanger and will move heat into the home which will increase humidity far beyond anything a dehumidifier will take out. The humidity in his home is not from humidity outside alone. It is being created by the luke warm air being circulated through his 76-78 degree house.

You're spot on, 03Lightningrocks. The fresh air controller opens the damper, then turns on the blower w/o manually energizing the coils to circulate air. If the AC or reverse pump heat happens to be running, then lucky me. Otherwise, not so much. Based on the ASHRAE math, the dampers open for 13.5 and 16.5 minutes per hour for each zone before I messed with the schedule.

I was just thinking of something in the shower. What if I disable the schedules and rig the units to open up the fresh air damper to 1/3rd every time the air handler blower turns on via the thermostat, then have the damper close back up when the blower turns off? That would ensure a very small mix of fresh air with recirc air every time the AC/heater turns on. Would that solve the problem? Or would getting rid of the fresh air units and going for a standalone ERV be a better solution?

This is how I would approach it. Heck, even if the dampers were full open when the system calls for cooling it would be better than the make up air units calling for the blower with no AC running.This time of year the AC is going to cycle enough to bring in plenty of make up air anyway. Allowing that control to bring on the blower with no ac on is killing your humidity removal.

Just an FYI that you may have already figured out. When temps outside are mid seventies and below like in fall and winter, the way the unit is working now works great. Truth is, you need the fresh air more in the winter/fall anyway. But that configuration for the summer is just awful in a climate like Texas..

Readinng this on the instruction sheet leads me to think this setting disables the make up air from calling for the blower. I would have to spend some time studying this option and how it would work with no remotes. I am thinking setting this switch to off is key to setting it up like you mentioned above. In the fall you can switch it back to on so you get some fresh air circulating when when the heat system does not cycle as much On 70 degree days and below you should not have an issue with humidity. Heaters don't run nearly as often as the AC in our area so allowing the make up air to run would help keep the air from being stagnant.

7 Switch On (optimal ventilation)
Override
Off (Remote Only)
On (optimal ventilation) – W8150 ventilates, based on control settings.
Override – W8150 runs ventilation continuously.
Off (Remote Only) – W8150 supplies ventilation only when there is a
remote call.

I was just looking at the diagram for using a remote. The two terminals labeled for the remote look like they are designed to go to a switch. You can check this by turning the switch to off and then check the voltage at those two terminals. If you are getting 24V it means that this connection is designed to call for the make up air when a switch of some sort completes the circuit. I point this out so you don't send 24v to those terminals from the ac blower. You can verify this by jumpering the terminals if you read 24v on them. It should turn the make up air blower on when jumpered. If this is the case, a relay can be installed that is energized off an accessory terminal providing 24v from the blower. Just be sure this accesory terminal only sends 24V when the system calls for cooling. If it sends 24V when calling for cooling or heating it will still work. Then you have the option of leaving it set to remote or on if you like it coming on more in the cooler seasons. Set it for remote in the cooling season and set it back to on for the heating season. When the contacts on the relay close, it should bring on the make up air unit.