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My house has an existing forced-air heating system and I'm looking at getting central AC added in a few weeks' time (indeed, I've booked contractors for estimates next week). An AC system would keep my house cool when it is hot outside.

...but what options are there for cooling a house when it's also cold outside (without running expensive AC)? I don't like having to manually open windows, so I was wondering if there was some kind of additional cooling system which sucks in cool air from outside and blows it through the forced-air ducts, thus cooling down the interior without needing to run AC.

...does such a system exist? Do AC systems do this anyway?

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    If outside air is coming in, it's gotta go out, which means opening the windows. AC works with closed windows because it's recycling interior air. Moving outside air inside displaces interior air, which has to go somewhere. – iLikeDirt Aug 18 '15 at 14:22
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    @iLikeDirt Most people's houses aren't as air sealed as yours ;) – Mazura Aug 19 '15 at 1:33
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    @Mazura my house is a new construction, my agent told me that the house is essentially hermetically sealed and I will suffocate if I don't let outside air in occasionally. Eeeep! – Dai Aug 19 '15 at 1:38
  • Then you need a fresh air intake, an economizer, or an HRV. – Mazura Aug 19 '15 at 1:49
  • If that is true Dai then it was irresponsible and likely against code (i.e. illegal) for the builder not to include an HRV or always-on exhaust fan. You may be able to have them pay the cost of rectifying this problem. – iLikeDirt Aug 19 '15 at 2:32
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There is an optional add-on part for HVAC systems called an economizer.

An HVAC economizer is a dampered vent designed to save energy and give the cooling system a break. Sensors within the economizer compare the outdoor temperature and humidity with that inside the building. –Google

When you call for cooling, the unit decides if it needs to run the AC or just open the economizer to pull in outside air.

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    Are there economizers available for residential applications? Are they also available for split systems? How do they exhaust the indoor air? – Tester101 Aug 19 '15 at 0:21
  • @Tester101 For split systems IDK; I've only seen them on roof top units, though I don't see why you couldn't. They basically just open the return chamber to the outside and suck in some air, which in all but the most recent means of airtight construction, finds its way out through all the cracks, no problem. It's about the same as a fresh air intake, except these are automatically controlled. – Mazura Aug 19 '15 at 1:10
  • I should clarify and should have stressed 'optional'. I've seen them for units, but no one ever asks for it and I've never put one in. It's a box with a motorized lover and a booster fan that you strap to the outlined hole that you punch-out for it. All the 'brains' will be integral to the unit, so you should specify your request for one. Ad-hocing it into an existing system may prove difficult if it wasn't designed to accommodate one. – Mazura Aug 19 '15 at 1:22
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You're looking for the V in HVAC (Ventilation). There are indeed systems that will pull in outdoor air, filter it, and supply it through the home. These systems would likely be in addition to any heating or cooling equipment, not as a part of them. To be specific, you're looking for a balanced ventilation system.

Talk to your local HVAC company, they should be able to recommend a system that will work with your existing equipment. They should also be able to provide you with an estimated cost of installing such a system.

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The term you're looking for is "whole-house fan". It's a big fan that can blow outside air, inside. I have one in my house and they work very well for your use case. Be warned that whole-house fans are notoriously difficult to insulate and air-seal. When winter rolls around, the last thing you want is a huge hole in the side of your house through which frigid air can easily enter.

Furthermore, you'll have to open your windows. But this is unavoidable anytime you want to draw substantial quantities of outside air into your house; it has to escape somewhere. With the windows closed, the air will escape through random cracks in your house, but only so much can escape that way. To properly exhaust the volume of air you would need to push through your house to actually meaningfully drop the interior temperature (a lot; like 3000 CFM), you would need to punch a huge home in your wall somewhere--otherwise known as a window. :)

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    A whole house fan is a bit different, as it typically requires the windows to be open to work. A whole house fan is just a giant fan that blows air out of the house, the makeup air is drawn in through open windows and doors. The type of system the OP is looking for, will have a dedicated intake and likely filters. At least that's what it sounds like "I don't like having to manually open windows..." – Tester101 Aug 18 '15 at 14:00
  • True, but the OP isn't going to get what he wants without opening the windows anyway. Outside air entering the house displaces interior air, which has to go somewhere, especially at high CFM levels which will overwhelm the ability of the air to exfiltrate through random cracks in the building envelope. – iLikeDirt Aug 18 '15 at 14:23
  • A Balanced ventilation system will have both a supply and exhaust, so there's no need for open windows. – Tester101 Aug 18 '15 at 15:03
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    True, but a ventilation system doesn't move much air, so it won't be much use for cooling. The conditions where using outside air for cooling is effective typically involve a low delta-T (say, 80f inside due to solar gain and 70f outside), so you need a high amount of air movement to meaningfully affect the interior temperature. A high amount of air movement means it's more of like the "AC" then "V" in HVAC. Ventilation is for fresh air, not cooling. – iLikeDirt Aug 18 '15 at 15:28
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    I live in a sunny, high-altitude high desert area where my own house often experiences the condition of a hot house with cooler outside temperatures at night and in the early morning. I can attest to the fact that ventilation alone doesn't cut it. I run my whole house house fan during this time and it's capable of lowering the interior temperature a few degrees. The OP lives in Redmond, WA, which is cool and cloudy. I am very surprised to hear that a house in that area could be substantially hotter than the outside temperature. Maybe there is substantial interior heat gain. – iLikeDirt Aug 18 '15 at 16:14
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I have had these systems installed on commercial applications. The system principal working method , Outside air is measured in temperature, i.e. the cooling system is calling for 74° and the exterior temperature is 63, two separate ventilation systems open, The forced air to supply your house with the cool air opens and the fan turns on. A second, exhaust system opens up to allow over pressure to release from your home. Essentially these are two VAV boxes one with forced air "supply" and one with Variable louvers. " exhaust" The controls are then integrated into your existing thermostat system. The controls are then integrated into your existing thermostat system

. I am getting ready to install one of the systems into my home, it will be makeshift due to the type of split system I already have but it is possible. If you explain to your HVAC contractor what you are after they probably could devise something for you as well.

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