I have automated Velux skylights that open and close based on outdoor temps, Indoor CO2 levels, and humidity levels. I’ve read conflicting opinions that the skylights should be closed when running AC as the interior of your house is pressure balanced for the AC and that opening them (to exhaust humidity or heat) actually causes an AC system to underperform. Does anyone have any thoughts/experience on this?
Ps I’d also love to connect them to HE but I think it’s only possible through third party methods.
can you share how this is done? We have Velux too but our system only allows manual open/close (or timed) using the remote(s). If it's not hard to do, I'd love to have it open/close based on temp (or at least close).
Regarding connecting to HE, if you figure it out let me know. It seems possible but non-trivial....
I Have Velux skylights although they aren't vented. Your home does not require outside air to properly use your HVAC system. In most cases I've been told that most residential HVAC system are undersized on the air handling issue. In many cases there is back pressure issues in the ducting that delivers cool air to your rooms and the furnace fan motor is under load trying to deliver that output. Also dependent on the contractor there may be issue in the return air ducts where there could be restrictions also.
Bottom line most homes probably are slightly undersized in their ducting. That area around the skylight can be very warm inside. Even with low e glass there is heat gain issues. In a situation where you aren't using the air conditioner, an open skylight which is venting can help exit out that hot air as long as there is other air filtering into the home from open windows, doors, etc. But in a closed system however, opening up that skylight is going to provide minimal air flow since everything else in the house is closed up. You also have a hot roof with surface air temperatures considerably higher than outside ambient air temps. Add the effect of air flow on that roof and air patterns, you could truly be inducing hot air into your home and the humidity in that air.
Also understand dependent upon outdoor air flow you may have some exhaust but again with no air coming into the home, outside air will come into your home through places which are not air tight. This could be from poorly fitting door, poor caulking around windows and electrical outlets.
My advice is if you want to maximize the performance of your air conditioning system, leave the skylights closed.
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We have the Solar Velux Active system with Netatmo. I’m not sure about your systems compatibility, but we have a hub that connects to our network and have several wall sensors that communicate with the skylights and an app.
Currently, you can only control it with Google Home by voice command. They promised Alexa/Echo control over a year ago but it never materialized. I’ve read you can run them through a Logitech Harmony Hub, but honestly I hate mine and it’s been sitting in a box for over a year.
As a side note (in case this helps others): because the skylights have a small solar panel, we received a federal tax discount last year on them as well as part of our roof replacement itself. I also had found a roofer that was willing to install them at a very low price ($100/each) And he got a further discount through Home Despot. Think it ran us ~$1,000/each which isn’t much more than ordinary skylights and we feel they were well worth the money as we needed replacements anyways. When you factor in the roof replacement, it was like no cost to us with the benefit of better air quality.
Thanks for the pointer, we have a few solar powered and a few electric skylights but not the active add on (which I didn't know existed). It looks like it can be added to existing installations so I'll have to check that out... it would definitely be nice to integrate into HE. I wonder if IFTTT would help?
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Thanks for the detailed reply and explanation. I’m wondering if temp venting on these are more beneficial in the spring and fall.
I installed a Panasonic ERV this summer that’s capable of 40 CFM but also have older, leaky doors that will be replaced. I also have a Panasonic Whisper Bath fan upstairs that has a low continuous venting per newer IAQ (indoor air quality) codes. So I think I already have a little bit of a stack effect happening as I do want some fresh/healthier airflow.
I do like the fact the the inside blinds of the skylights auto-close based on weather conditions saving additional money and comfort. Many times we were cooking or the CO2 levels were high and the skylights opened Automatically which was pretty nice. I think we forget too that too much leak-free building can actually lead to illnesses/sick building syndrome as well.
The humidity auto venting part of the app is confusing to me. I always associate humidity falling and not rising but I suppose I have that backwards?
One thing I will say is that Netatmo has almost non-existent tech support in French. When you ask Velux, they refer back to Netatmo and a few Velux reps have even hinted that they’re difficult to work with. I’ve tried asking these questions before and hear only crickets.
I’d double-check with them assuming their phone lines are open. I think they work primarily via RF so they could be be easily backwards compatible. Velux customer service has been very good in the past.
An ERV is a balanced ventilation device. The quantity of fresh outdoor air that it draws in is approximately equal to the quantity of indoor air that is pushes out. It neither pressurizes or depressurizes your house relative to outdoors.
This is called exhaust ventilation. The fan pushes indoor air out, depressurizing your house. Air will come in somewhere else. Where it comes in depends on where the biggest holes are. Assuming you don't have any gaping holes, then that would likely be at your skylights when they are open. In other words, since you have exhaust ventilation in your house, you are likely drawing air in through the skylights instead of allowing air out.
In winter, stack effect draws air in low in your house and out high in the house. (Chimneys rely on stack effect.) In summer, that is reversed. Stack effect will tend to draw air in through high openings and let it out through low openings.
Unless you provide mechanical ventilation - like your ERV and continuously running bath fan.
