Whole House Fan - So far so good.

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Which brand? Ive used the mitsubishi and fujitsus and was pretty impressed.


The older units are Sanyo. The newer ones are Panasonic. I wish I had gone Panasonic to begin with.

Mitsu makes a great system. Daikin is good as well. They are all similar in the way they operate but the more advanced systems have all the sensors and intelligence built in. The Panasonic can detect how many people are in a room and adjust the cooling accordingly. If I am the only person in the room it directs the airflow more in my direction. It also purifies the air.
 
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At the house I have mentioned we installed mini splits. There are six units since we have multiple rooms. The setup has worked well because we selected units with sensors that detect when a person has left the room. The units spin down to a efficient setting and after a period of time turn off. Rooms like bedrooms are off during the day but will be occupied during the hottest part of the day sometimes. These are all inverter units as well.

They're a good retrofit for a house with no ductwork and for which you don't want to install any.

But I would not choose to have a bunch of minisplits (or even a multi-zone minisplit) over a central air system in a tight well-insulated house for the following reasons:

1)They don't have very good filters, and they seem to clog quickly, causing the minisplit to error out. My central air unit has a media filter that is Merv 8 rated, 25x20x4, and I can go over a year before I need to change it.

2)They have no provision for bringing outside air into the house. My central air unit has an Aprilaire fresh air intake system that has a duct to an intake on the side of the house, a damper, a fan, and a control that selects the amount of fresh air per hour in 5 minute increments. I currently have it set at 20, this keeps the radon level in my house as measured by an Airthings Corentium below 1 pCi/L. (This is "build tight and ventilate right" in action).

3)Sometimes I run the central air fan to circulate air through the house, especially in summer. This brings some of the cooler air from the basement upstairs. Can't do that with minisplits. (And my central air fan is an ECM so it runs at a low energy-saving speed in fan-only mode).

4)My central air system is zoned, I have two thermostats, one for upstairs, one for downstairs, both connected to an Aprilaire zone controller with dampers. I just have one air handler which handles both zones.
 
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They're a good retrofit for a house with no ductwork and for which you don't want to install any.

But I would not choose to have a bunch of minisplits (or even a multi-zone minisplit) over a central air system in a tight well-insulated house for the following reasons:

1)They don't have very good filters, and they seem to clog quickly, causing the minisplit to error out. My central air unit has a media filter that is Merv 8 rated, 25x20x4, and I can go over a year before I need to change it.

2)They have no provision for bringing outside air into the house. My central air unit has an Aprilaire fresh air intake system that has a duct to an intake on the side of the house, a damper, a fan, and a control that selects the amount of fresh air per hour in 5 minute increments. I currently have it set at 20, this keeps the radon level in my house as measured by an Airthings Corentium below 1 pCi/L. (This is "build tight and ventilate right" in action).

3)Sometimes I run the central air fan to circulate air through the house, especially in summer. This brings some of the cooler air from the basement upstairs. Can't do that with minisplits. (And my central air fan is an ECM so it runs at a low energy-saving speed in fan-only mode).

4)My central air system is zoned, I have two thermostats, one for upstairs, one for downstairs, both connected to an Aprilaire zone controller with dampers. I just have one air handler which handles both zones.


I agree. This house is overseas so the construction and availability led us to mini splits.
 
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I agree. This house is overseas so the construction and availability led us to mini splits.

A friend of mine had a window unit in his living room that was installed thru-the-wall. It was starting to fail, so I suggested he replace it with a mini-split that has a heat pump. (His house was built in 1965 with a boiler and radiators--a questionable design decision given that this part of the country has very hot and humid summers, and any forward-thinking individual back then would likely have realized that central ac would be more affordable in the future, making the installation of forced-air furnace and ductwork a sensible thing to do, allowing for a fairly easy upgrade in the future...)

(as a side note, sometime in the 70s, my dad installed central ac on the furnace in the house we lived in back in Lombard, IL -- he said there were DIY kits to do it back then!)

In that situation, a mini-split is a major upgrade to a wall-banger or window-shaker. Especially one that's also a heat pump.

He got a two-ton minisplit and aside from a few times it shut down due to a dirty filter, it's been working great...
 
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We've finally discovered the ceiling fans that are in every room of our house. I always thought they were to circulate air when it's warm to keep the warm air down. They do a great job of keeping you cool in the summer too! We were running the central air a lot this summer until we discovered the ceiling fans.

Being a mobile home, no attic for us to do a whole house fan. A former coworker of mine had one and said it worked great.
 
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Attics in Texas get miserably hot, and it would seem counterintuitive to put in the HVAC air handler up there, but that's where mine is.

Got a new AC system put in several years ago, and the HVAC guy suggested I get attic fans cut into the roof to relieve the heat soak of the air handler. The roof already has vents, along with soffit vents, so I just bought a big industrial fan and mounted it to suck air up through the attic entrance, which is in the garage, and set the garage door opener to stop 2 inches before fully closed. Haven't measured the temperature difference, but I know that you can go up there now and actually be up there for a few minutes without feeling like you're going to die.
Due to the soil conditions basements were not popular and builders don't want to sacrifice interior living space for a proper mechanical room because it would require enlarging the footprint of the house which means a higher price tag so the HVAC went into an unconditioned attic. This allows the homeowner to pay for the lack of energy efficiency while the builder still gets to sell the house at a lower price. Definitely a win for the builder.
 
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Above is a study, Florida-based, of whole house fan cooling.
They were more popular before air conditioning became common.
Ya. They're a bad idea and they don't work in all but the upper elevations and upper latitudes.

I like how the article mentions how people survived prior to in home air conditioning. People survived prior to indoor plumbing as well.<sarcasm>
 
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Attics in Texas get miserably hot, and it would seem counterintuitive to put in the HVAC air handler up there, but that's where mine is.

Got a new AC system put in several years ago, and the HVAC guy suggested I get attic fans cut into the roof to relieve the heat soak of the air handler. The roof already has vents, along with soffit vents, so I just bought a big industrial fan and mounted it to suck air up through the attic entrance, which is in the garage, and set the garage door opener to stop 2 inches before fully closed. Haven't measured the temperature difference, but I know that you can go up there now and actually be up there for a few minutes without feeling like you're going to die.
FIRE CODE?
 

UncleDave

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Ya. They're a bad idea and they don't work in all but the upper elevations and upper latitudes.

I like how the article mentions how people survived prior to in home air conditioning. People survived prior to indoor plumbing as well.<sarcasm>

Its situational.
It works better than nothing in humid areas.
It works great in dry areas with at least 10degrees diff in in and outside temps.

Its not an AC replacement but separate system that you have to manage.

Conclusions

Based on our results, we can draw some conclusions relative to natural cooling potential and the use of whole house fans in hot and humid climates:

  • Local wind velocities will often not be great enough to provide continuous comfort using natural ventilation in a typical built-up suburban environment. Forced ventilation will be necessary to provide effective ventilation.
  • Massive buildings offer improved interior comfort only if the building can be strongly ventilated by mechanical means at night or if breezes are adequate during the evening hours.
  • Nighttime use of whole house fans offer significant potential to enhance natural ventilation when evening wind velocities are low. Interior temperature reductions of 3 - 6oF are possible, even during the hottest weather.
  • Ventilation of homes using whole house fans may do best to draw air from the warm kitchen area.
  • Consideration of moisture levels can serve to significantly reduce the potential of whole house ventilation in humid climates. Use of a whole-house fan during nighttime hours was measured to increase interior relative humidity by approximately 10%.
  • Measured daily whole-house fan energy consumption varied from 3.2 - 4.2 kWh when used 12 hours per day. This compares to a sub-metered air conditioning energy consumption averaging 36 kWh/day during the previous summer. However, the achieved comfort levels of the two modes of cooling were very different and do not lend themselves to a meaningful comparison.
 
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Its situational.
It works better than nothing in humid areas.
It works great in dry areas with at least 10degrees diff in in and outside temps.

Its not an AC replacement but separate system that you have to manage.

Conclusions

Based on our results, we can draw some conclusions relative to natural cooling potential and the use of whole house fans in hot and humid climates:

  • Local wind velocities will often not be great enough to provide continuous comfort using natural ventilation in a typical built-up suburban environment. Forced ventilation will be necessary to provide effective ventilation.
  • Massive buildings offer improved interior comfort only if the building can be strongly ventilated by mechanical means at night or if breezes are adequate during the evening hours.
  • Nighttime use of whole house fans offer significant potential to enhance natural ventilation when evening wind velocities are low. Interior temperature reductions of 3 - 6oF are possible, even during the hottest weather.
  • Ventilation of homes using whole house fans may do best to draw air from the warm kitchen area.
  • Consideration of moisture levels can serve to significantly reduce the potential of whole house ventilation in humid climates. Use of a whole-house fan during nighttime hours was measured to increase interior relative humidity by approximately 10%.
  • Measured daily whole-house fan energy consumption varied from 3.2 - 4.2 kWh when used 12 hours per day. This compares to a sub-metered air conditioning energy consumption averaging 36 kWh/day during the previous summer. However, the achieved comfort levels of the two modes of cooling were very different and do not lend themselves to a meaningful comparison.
For sure. They work in low humid environments best. The funny thing is that study, iirc, was commissioned in 1992. HVAC equipment today is significantly more energy efficient than what it was back then. Of course they only measured energy usage for summer time cooling. What about winter time heating when heat leaks through the fan into open air outdoors (i.e. vented attic).
 

UncleDave

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For sure. They work in low humid environments best. The funny thing is that study, iirc, was commissioned in 1992. HVAC equipment today is significantly more energy efficient than what it was back then. Of course they only measured energy usage for summer time cooling. What about winter time heating when heat leaks through the fan into open air outdoors (i.e. vented attic).

Florida has little concern for cold air for sure.

If your attic is already vented, then a fan in the gable just sitting there doenst hurt.

The damper on my system is pretty good- R5 Other spots will leak more than that will.

Where most poeple get this wrong is the amount of net inches of ventilation they need to make either a WHF or Attic fan work.
 

UncleDave

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Whole house fan whitepapers are rare. Ive been finding a few though.
 

Al

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Remember that to make ridge vents effective you need to provide internal natural circulation like having soffits with holes.
 
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They really went to work cutting big squares into those joists. Guess they didn't want bulkheads and would rather compromise structure for aesthetics.

It may appear that they compromised the structure but the manufacturer of the I-joist likely approved that design, so an engineer somewhere knows that it didn't compromise the structure.
 
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