You have 3.5 tons for a 2,000 square foot well insulated house in Canada?
I’d say you have oversized equipment.
Hi All,
i've read around a bit and talked to my installer about my problem but we can't really put our fingers on a solution. I'll throw all the info I can think of here, hopefully you'll have everything to help me.
Here is my setup
New construction, walls and roof closed and heated since December. I live in Qc, Canada. 4 inch foam (omega) all around the basement. R60 roof, R 27 walls.
Two story with finished basement. ~ 960 sqft per floor, all open area except for the 2nd floor which has 3 bedrooms, a laundry room and a bathroom.
PAYNE AC PH15NB042
HEATER : PF4NMB043
CARRIER KFCEH3291F20A
ECOBEE3 Lite to control the system
The temperature setpoints are respected perfectly, but during the day the humidity varies from 57 to 70%, and usually stays in the 65% range. It is 28C (82F) during the day and humidity is ~60s-70s. I have turned off the heat exchanger a week ago and only start it when showering.
During the day the setpoint is 22C / 72 F, during the night i like to bring it down to 19C / 66F. I will always hit 70-72% during the night. sometimes i wake up uncomfortable due to the cold and humid air. It reached 75% the other night.
At first my reflex was to have the fan run more so i tried increasing the fan minimum runtime from whatever was set first (30 or something) and lately it was set at 55. didn't help my problem but can't really tell if it made it worst, maybe? So lately its been on AUTO+minimum 55minutes/hours read below...
My mechanical room is 6' x 20' and contains ducts, pipes, one fridge, one freezer, water heater (electric), and it gets so cold and humid that condensation is present of the ducts and the PEX water lines drip on the floor as well.
I now added a dehumidifier in the mechanical room to help.
After looking on the web, i've read that trying to reduce the fan usage might help, so I changed my approach on that regards and brought it down to AUTO+10minutes/hour minimum. I've done this last night, humidity as we speek is 64%.
Thanks!
You have 3.5 tons for a 2,000 square foot well insulated house in Canada?
I’d say you have oversized equipment.
“I haven’t failed. I’ve just found 10,000 ways that won’t work.” - Thomas Edison
“It’s not whether you get knocked down, it’s whether you get up.” - Vince Lombardi
"In this house we obey the laws of thermodynamics" - Homer Simpson
Local 486 Instructor & Service Technician
Sizing isn’t done via square footage.
Basements often only need dehumidification and a small amount of heat. And shouldn’t be on the main hvac system.
“I haven’t failed. I’ve just found 10,000 ways that won’t work.” - Thomas Edison
“It’s not whether you get knocked down, it’s whether you get up.” - Vince Lombardi
"In this house we obey the laws of thermodynamics" - Homer Simpson
Local 486 Instructor & Service Technician
R I P Icemeister
Supporting our Vet’s
http://www.soldierride.org/
http://www.woundedwarriorproject.org/
I don't think so, but even if its oversize, how much more oversize would it be? a 3.5 instead of a 3 would really make that much difference in regards to humidity?
15% over may make the difference. It will explain the lack of dehumidification but, Suppose you only needed 2.5-Tons now your 30 % over!
Bet you that unit doesn't run more then 15 - 20 minuet cycles during the heat of the day. As it get cooler the situation will only get worse.
R I P Icemeister
Supporting our Vet’s
http://www.soldierride.org/
http://www.woundedwarriorproject.org/
Welcome!
Glad to hear you have fresh air ventilation and a well insulated home.
You need a couple more things.
Start with a properly functioning and setup a/c.
On hot day where the a/c is operating more that half the time, the a/c should be removing enough moisture to dry the home to <50%RH. Properly charged and adjusted, they will. The moisture levels you are getting is the results of the moisture from infiltration/ventilation air, the outdoor dew point, and the internal moisture load from occupants minus the moisture removed by the a/c. The amount of moisture removed by the a/c depends on the temperature of the cooling coil as the homes passes through it. When your a/c installer starts the a/c, the air flow is adjusted to provide the moisture removal needed. The moisture level of the air is the dew point of air. At 72^F, 50%RH, a 52^F dew point, your supply air needs to be 46^F dew point to remove enough moisture to maintain a 50%RH in the space. Your a/c tech will understand all of this.
Get the tech back and adjust the air flow.
NOt a good idea to cool space far below the outdoor dew point for the 66^F, 50%RH, a 47^F dew point. You will be causing condensation in the exterior walls of the space when the outdoor moisture meets the 66^F temperature. Better warm the stat to 70^F during peak outdoor dew points.
You will find the 70^F, 50%RH, a 50^F dew point more doable and comfortable. Anyway, warmer is better for equipment and structure. But it is your home.
You should be able to operature your HRV when the space is occupied at a fresh air change in 4-5 hours also.
During evenings and rainy days, your a/c will not run enough to maintain 50%RH. The %RH will be dependent on the outdoor dew point of the fresh air and how much moisture the occupants add.
Your can have 50%RH even on a rainy day by adding a small whole house dehumidifier to your a/c ducts. Like an Ultra-Aire 70H which will remove upto 70 lbs. of moisture per day when the a/c does not run enough.
Keep us posted on how this all goes.
Regards Teddy Bear
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"
I just looked up my ecobee monitor and i clearly see that when the AC is running the Humidity goes down quickly. Usually a 9PM the AC starts for 1.5 hours to bring the temperature down and humidity drops by 10-15 even 18% sometimes. but within the next hour the humidity goes back up to nearly 10%, and within the next 3 hours its back at its starting level.
I would post a picture but I'm not allowed since i'm new here and I don't have enough posts.
Thanks,
My config is as follows :
6 AM - 10 PM setpoint is [20C-22C]
10 PM - 6 AM setpoint is [17C-19.5C]
What i see is that during a day where the outside goes from 21 in the morning to 28 during the day, the AC will not start very often. I see days that it doesn't start at all, sometimes it starts 30 minutes at around 4 PM.
at 9 PM, the AC goes on for 1 hour to bring the current temperature down to 19C for the night. the Humidity % usually goes from 65-68 down to 52-54%. within the next hour or two, the humidity will climb back up 10%.
To maintain the temperature at night the AC cycles on for 15-20 minutes per hour, everytime dropping the humidity a couple of %, but once it stops the humidity goes back up.
You can send me a PM with your email address and i could send you the charts.
It sounds like an oversized units behavior.
“I haven’t failed. I’ve just found 10,000 ways that won’t work.” - Thomas Edison
“It’s not whether you get knocked down, it’s whether you get up.” - Vince Lombardi
"In this house we obey the laws of thermodynamics" - Homer Simpson
Local 486 Instructor & Service Technician
Could I be at a point where I have ran the fan ON too much time and there is a big amount of humidity accumulated in the house, and humid air takes longer to react during the day hence the fact that I have a good temperature stability throughout the day that doesn't require the AC to go on?
Maybe I should rent a dehumidifier and have it remove the excess moisture in the house and then the unit might behave a little better? I don't know?
I just checked the detailed report, at night it cycles on for 10 minutes per hour to maintain the setpoint.
Again, your unit is displaying every sign of oversizing.
Running the blower constantly will increase humidity more.
You likely need smaller equipment.
“I haven’t failed. I’ve just found 10,000 ways that won’t work.” - Thomas Edison
“It’s not whether you get knocked down, it’s whether you get up.” - Vince Lombardi
"In this house we obey the laws of thermodynamics" - Homer Simpson
Local 486 Instructor & Service Technician
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"
“I haven’t failed. I’ve just found 10,000 ways that won’t work.” - Thomas Edison
“It’s not whether you get knocked down, it’s whether you get up.” - Vince Lombardi
"In this house we obey the laws of thermodynamics" - Homer Simpson
Local 486 Instructor & Service Technician
My concern is that oversized or not, since the unit doesn t start at all during the day, a smaller machine would not help. It might bring the humidity down when transitionning to night time temperatures but the humidity problem would persist during the day.
On a side note, fan is on auto and minimum 5 min/hour, i blocked 75% of the intake that is taken from the mechanical room itself to increase the air intake from the 2nd floor rooms, and the dehumidifier i’ve added to the mechanical room removed 3-4 liters of water yesterday and 2-3 today. Humidity when up to 64 today which is slighly better than usual, and its currently down to 52 as we speak (10:45 pm, so right after the cooldown period for the night).
Second side note : 64% was still way too humid today, not comfortable at all.
Very important thing I just remembered, Ecobee collects data and compares it with other people that are in the area. with a month of data, my home is in the top 17% in terms of energy efficiency(insulation).
Open question, should I get a smaller heat pump AND add a dehumidifier to the system that would allow me to recirculate the air continuously (or more often) to fix my problem?
This is a description typical a/c taking moisture from the air and loading the cooling coil/pan to the point of going down the drain. With a dry coil, this takes 15-30 mins. depending on the size of the coil.
As you described, the stat is satisfied If the fan is "on", the coil dries to the space in <1 hour. The couple lbs. of moisture on the coil is enough to raise the indoor %RH 10%. With fan in "auto", the drying process takes a couple hours.
As you see, fan "auto" slows the re-evaporation of moisture from the coil, but does not fix the problem.
All things considered, you have reduced the sensible cooling load to the point that the a/c does not run enough to remove the latent load. The latent load is moisture from the occupants and infiltration/ventilation.
The first check is recheck the air flow while a/c is cooling. We need to have a cooling coil that is 30^F colder than the return air temperature. 72^F requires 42^F coil temperature checked by a qualified tech. When the evening temperature is functioning, the coil 33^F to remove enough moisture to do it's part in removing moisture to reach the 50%RH level. As you see this is near freezing and not recommended. I suggest raising the evening temperature to 70^F until we get the humidity under control. This means you need 70^F minus 30^F, a 40^F coil temperature. This adjustment to the air flow reducing the coil temperature increases moisture removal and estends the run time cycle. This will lower the %RH in the space.
The ultimate fix is maxing the dehumidification and adding a small whole house dehumidifier. A unit like the Ultra-Aire 98H or XT105 correctly connected to the a/c would assist the a/c properly setup a/c in providing 50%RH while the outdoor dew points are plus 50^F.
This extremely well insulated structure and extreme low temperatures requires careful attention to every detail.
Welling to talk to the a/c contractor the details.
Regards Teddy Bear
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"
Thanks for the tips, i will look into that with my installer.
Two more questions,
the mechanical room has a 18 x 18 grill that allows air to pass, since its located in the bottom of the staircase, it sucks air from thr basement and the main floor (which is all open space). all the air going through is being pulled by the 12x12 opening in the return duct. For the second floor returns there are 3, one in each room (12x6 if i remember correctly). 2nd floor Bathroom has one return but it goes in the air exchanger, along with 1st floor bathroom. my question is : would the air being sucked from the 3 bedrooms be enough for the dehumidifier ?
Looking at the installation diagram, it takes outside air and is a kind of complicated installation, taking into account that I have a air exchanger located in the mechanical room that just sucks bathroom air out and bring new air in the mech room, would I have to connect them together or just the return air of the 3 bedrooms would go through the dehumidifier?
Can I connect it to an Ecobee device that would run the Fan alone and the dehumidifier to control the humidity even if the temperature setpoints are reached? (i know ecobee 3 and 4 does it, but would it be compatible with the dehumidifier you specified and the way it will be hooked to the current system?)
Last question (for now), if I end up doing all this, would you suggest me to ask my installer to replace my 3.5 tons heat pump? for what? a 2 or 2.5?