Automatic Whole House Fan???
 

Hello Everyone. I've been lurking for a year or two, but this is my first post. If I've posted this in the wrong section, please let me know and/or move the thread.

I have a project that I'd like to run by the EcoRenovator community to see if anyone can point me towards some resources. Please bear with me as I explain.

I live in Denver, CO, and have a down draft evaporative cooler installed. When cooling is necessary, I don't like to turn on the pump, but rather turn the fan on at night to cool the house, and turn it off during the day when it is hot outside. This works very well to keep the house comfortable, and avoids the muggy air created when the pump is on.

There are, however, a few problems with the situation as it stands:

1) The cooler isn't well filtered, so the fan forces a lot of dirt into my house, which reduces air quality and requires extra cleaning of the walls and ceiling near the vent.

2) The fan isn't controlled by a thermostat. If the air outside is warmer than the air inside, then I'm heating rather than cooling. This means that I have to be home, awake and attentive to switch the fan on at night and off in the morning at the right times.

3) The venting isn't baffled, requiring that I insulate it and air seal it in preparation for winter. I also gain a lot of heat through the vent when the fan isn't running during hot days.

4) My house has a flat roof, and I've put a lot of effort into rehabbing it, form the outside in. The swamp cooler really ruins the roofline and since I don't use it as it was designed, I see no reason it should stay. Sure I'm concerned with aesthetics, but at least I listed it #4. Right?

SO... my solution, if it's possible:

Remove the swamp cooler. Install a HEPA filtered whole house fan with an automatic insulated baffle. Use the same 14" square ductwork currently employed by the cooler. Then either source, or program/build myself, a thermostat that acts to automate the fan and baffle system, using multiple thermometers.

The thermostat would open the baffle and activate the fan if the outside temp were lower than the inside temp, and if the inside temp was above a programmable temp floor. The fan would shut off and the baffle would close once the air outside became warmer than the air inside, or the temperature floor was reached.

I have a list of questions that I'd love some input on.

1) Where could I source a filtered, baffled, whole house fan for 14" square ductwork? Or, are the filter, fan and insulated baffle separate purchases?

2) I am planing on using an Arduino and two thermometers to build/program the thermostat, unless anyone here has a better idea.

3) Are there any online resources that you think might be helpful? I'm having trouble finding anything.

4) Would you call this a pipe dream? It seems reasonable to me, but I'm no HVAC expert.

For those of you who made it this far, thank you for your time.

Also, thanks in advance for any help.

Justin

Welcome to the world of non-lurkers Justin, we're glad to have you here.

What you are proposing shouldn't be that difficult to do, however it will be a bit of work especially if you haven't done something like this before.

For the ducting you may have to end up making something yourself. I'm not aware of any whole house fans that are made to hook up to ducting. In fact, most of them are just designed to pull air out of your house and into the attic, not blow into the house. I'm not sure how much benefit the ducting provides, but you may not even need it.

Another thing to think about is a whole house fan requires something to suck air through. Yes, there is the opening for the fan, but a window or something else must be open to suck air through too. How do you plan on automating this? I have seen guys use electronic actuators to open and close windows automatically so it can be done.

The arduino is an excellent selection for making a controller for this project. I currently have an use one for basically the reverse of what you're doing (I use mine to blow hot attic air down into my house for heating during spring/fall). I documented my project here. You should very easily be able to use my exact setup and just a little reprogramming for your needs.

This should work, since Denver has a higher elevation you can get the benefits of cool nights and as long as the humidity isn't high in Denver, which I assume its not with the swamp cooler, then it makes it a viable solution. This should be fairly simple to install, the automation part will be the challenge.

Be sure that you have some form of automated opening controlled by a damper for the outside air to come in. Ventilation only works if outside air can come in.

Pop in and look at the "AirScape" site that appears on your post. The photos and descriptions should provide some ideas and inspiration.
Also, if you can find an opportunity to look in/at some commercial or industrial air handling equipment you may also get some ideas. That industry uses a wider selection of equipment, and combinations of equipment than is normally seen in residential installs. Most residential equipment has a "consumer packaged" kind of character about it, many parts are not interchangeable, and they may be "multitask" in nature.
As far as the aesthetics of your roof top equipment, maybe take another cue from the commercial industry: cosider installing a privacy panel or valance in front of your equipment, picking up on styling elements from the rest of your house. The shade from the panels may be helpful to the operation of your equipment as well.

I have been considering this as well for my whole house fan. There was a nice discussion here, about using a stamp microcontroller with dual relay and two thermistors. Total cost about $70. There is also a link there to an arduino-based DIY controller.

Justin: just wondered if you had made any progress on your controller since your post?

Rick

You should be able to do something similar using any PC, a script or two, and a few X10 devices/one wire temp sensors.

Only X10 device I'm familiar with is a webcam. I will do more investigation..
Also, I would like to use two sensors with some sort of code to compare difference >5 degrees (inside), before the fan kicks on. And then a timer or comparator to shut off when the house temp equalizes with outside.

With X10 you can get a starter kit (shop around, their usual "sale" price is ~$100, but you should be able to get most of that for something like $40 or so) that has a usb or serial wireless transmitter to interface a computer via one of the RF receivers and a few modules/couple remotes. Control of the devices through a program like bottlerocket in *nix is pretty straightforward, and I think getting some one-wire temp/humidity sensors and writing a bash script using something like digitemp would be fairly straightforward too. The nice thing about a system like this is that it's very flexible and extensible. You can start with a simple whole house fan that would turn on when the windows are open and the outside temps are low enough, and expand that to something that can open/close windows, turn on individual fans, check the weather forecast, and even integrate something like a solar collector system into automated climate control.

You could use my DIY arduino design. I'm using it for a different project (using attic heat), but it would be incredibly easy to adapt. Its all spelled out here:

http://ecorenovator.org/forum/applia...ontroller.html

Otherwise there is some pretty reasonably priced ones that a guy sells here:

myDTC Temp Controllers and Solar Trackers Store - Temp Controllers

You could get two remote bulb t-stats with 20' capillaries and C (common) NC (normally closed) and NO (normally open) connections. These can easily be wired with 120v in series with your fan. Wire one through the NC connection to set your house temp and the other through the NO connection to measure outside temp. That way they both have to close the ciruit for the fan to run and you don't have to monitor anything.

Thanks Indyplumber.. This sounds like an ideal solution. The next step is to price out materials and set it up. Seems like it would be a more inexpensive solution than others I have been looking at. :thumbup:

The Tamarac (which is the only whole house fan you should buy!) has an IR or RF remote. Just use an IR blaster connected to a temperature monitoring device to control it. You could also have an outdoor temp sensor to compare values with the indoor unit so it only turns on when there is a lower temp inside.

If you already have a whole house fan and it's not a tamarac you should remove it and replace it.

40% AC Savings from using Whole House fan (Denver, CO).
I did a controlled manual test to see what % of savings could be achieved from an automating a whole house fan. Using zip specific Nat.Weather Service Data and my thermo as controls, my AC ran 41% less if I used Denvers cool night air to cool the interior thermal mass and air. I used a laser temp reader to show the huge difference in drywall, and brick temperatures by 6 AM. Because the Xcel Energy rate doubles in the summer months that utility savings would be $300- $350 per season on my house.
I have a layout that would allow me to draw cool air externally into my central HVAC return system, Mirv 12 filter it and distribute it -if I can get the controller unit . I've called 20 HVAC companies in Denver and cannot find anyone who has the knowledge to wire a temperature and relative humidity limited switch system to my central HVAC and whole house exhaust fan.
If you know anyone in Denver who knows how to wire it into an HVAC system have them contact me. When that kind of system can deliver $300- $400 per year cash savings , homeowners would be lining up. larryg7@arczip.com

What you need(in my opinion) is not a relative humidity switch but a switch that is based on the dew point. If it is warm and the humidity is extremely low, it might actually be a few degrees warmer in the house but if it lowers the dew point of the house, you'll be more comfortable, this is also more important if it allows you to dehumidify on a dry morning and close the place up and give the air conditioner less moisture to remove, if you need to run it on super hot days.

The temperature is usually easy because I imagine you can get a line voltage thermostat for that. Moisture is a tougher cookie but I imagine a line voltage relay connected to a dehumidistat would do the trick. ...but relative humidity is still not the number I would want to go by. In Minnesota we have a summer dew point for months at a time that keeps the windows shut unless you want to rot your walls and carpet, if you have a finished basement, which sucks. I know a bunch of people who open their windows anyway at night here but I can smell the mold, oddly enough they get used to it as it gets worse and think I'm crazy when I tell them that I can smell the mold stench on my clothes when I get home after leaving their house.

You need to do a little research on this...

There are many temperature sensors, and also many humidity sensors available, some even have both on the same precision chip. fo cheap.

There are loads of Arduino projects that will do this very thing.

Time to dust off the old thinking cap, and TRY_THIS.

-AC

The industrial equipment you're seeking is called an economizer. It rigs up to the return air plenum and reroutes the intake to your choice of supply. An economizer can also be rigged to exhaust stale air outdoors. Some economizer units come with their own differential controllers that make all the decisions and tell the units what to do and when. Or you can go with a zone damper, but they are usually controlled by a separate device.

Simply automating a whole house fan alone is not the answer. One always opens a window when running a whf. If you don't do that it won't work and it could cause havoc with things like an indoor gas water heater that starts backdrafting. I've thought about doing that myself. You would need a motor operated insulated damper to supplement the whf to automate the whole system. And perhaps an economizer too as was just suggested. Not cheap or easy but definitely doable.

Probably a more practical alternative is to only automate the OFF control. Then you wouldn't need a control damper. This would allow you to open the window, turn on the fan and when the house temperature got as cool as you set on the thermostat it would turn off automatically. That would be my guess as the best control solution for balancing the reward to amount of construction ratio.

Simple ideas are always harder than complicated ones.
 

I don't know what I was thinking when I said you needed a motorized damper to replace an opening window. Wrong. All you need is a backdraft damper. A doggie door for a large dog will do, though it isn't the most energy efficient. (you already knew that)

DOH you live in Denver
 

The blatantly obvious things are the hardest to miss. Just go to a hydro grow store and tell them what you want. Believe me, they will have it CHEAP or OUTRAGEOUSLY EXPENSIVE in sixteen flavors. Those growers need lots of fresh, filtered air. General rule: more cfm and quieter costs more.

While you're there, you can get a diff temp control for 20-30 bucks and up.

I'm glad this whole subject was brought up because it is really appropriate to my philosophy of using active solar heating and cooling in minimalistic ways. It sounds like a contradiction but I don't think it has to be. I'm really not sold on the passive house approach of forbidding ACTIVE controls for natural heating or cooling or, for that matter, eschewing installation of photovoltaic panels. I think their approach is too restrictive and makes it almost impossible to maintain a constant temperature range within 3 degrees F, plus or minus, of the desired temperature.

For instance, if you design a system for gaining window radiation shining on a dark colored slab it only works well for "average" days for your climate. It is likely to be too hot sometimes and too cold others. Their idea of insulating to maintain temperature is great but it only goes so far.

So I decided to go ahead with plans to install an automatic whole house fan in my house. It will complement the system I'm already installing that uses a radiant barrier in combination with two automated dampers to retain heat from the attic and bring it down into the house in winter. I'm insulating the house really well, not quite to passive house standards but pretty good, so I won't be putting a huge strain on my goal of keeping the house within +/- 3 degrees F of the desired temperature during the day. Who knows if I'll be successful but god is it fun trying:p

I'll post a new thread and put a link here when I've gotten a bit more organized. It will definitely involve Arduinos and a bunch of backdraft dampers.

I'll just make one more (off topic) remark about why I think Passivhaus is misguided in many of their restrictions. I'm not talking about their emphasis on insulation. They are always talking about using passive solar heat from solar heat through windows. That's all well and good if it never gets too hot but that's almost impossible. Rather than use windows that you really can't control much wouldn't it be better to use something else that absorbs solar radiation and then choose to admit or not admit it through automation.

It's not at all a matter of Passivhaus being purist. After all, what is a heat pump that heats or cools? It's an automated control system. Really, all Passivhaus is doing in their quest for purism is saying "you can use active systems for non-renewable energy sources but you may not use active systems under any circumstances for renewable energy sources."

That's just dumb. End of rant.