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Evaporative Cooler with Minisplits

braun247 | Posted in General Questions on

I get that mini-splits are all the rage.  I will have them in our new house, but in the Denver metro area, we are a Climate Zone B, which means it’s dry.

Most people from the East have never heard of an Evaporative Cooler and a lot of the articles written about cooling never include it.

I’ve used them my entire life. I could leave it on 24/7 and never see the cost in power or water bill.

Can Evaporative Coolers be included in new homes cooling load calculations (Manual S) and have the mini splits as a backup for the few days it’s too humid to use one?

From an energy standpoint, these are the best cooling options.

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  1. walta100 | | #1

    From the one house I have been in with a swamp cooler to me it did not seem to play well with the air conditioner.

    When we build a modern energy efficient home we built it to be tight and not allow air to enter or escape the building. The swamp cooler needed to replace 100% of the air from the house every 10 to 20 minutes to work.

    The house I visited has pressure operated vents in every room to vent air. It was not uncommon for a breeze to blow over the house and we could hear the vents open and I never got the feeling the vents sealed tightly when closed.

    The cooler itself would be another huge hole in your buildings envelope.


    1. Jon_R | | #2

      Or use an indirect evaporative cooler - the moist air is directed outside. Or direct the cooled/overly moist air into a HRV intake.

      1. braun247 | | #4

        I have never heard of an indirect EC. I will have to look into that.


    2. braun247 | | #3

      A planned hole is easy to have a solution to. That is why I want to think about it before being built. As for pressure vent, I have never heard of that. The 4o years I have been using a cooler, all we would do was open a few windows where you want the cooling to go. You also cannot run an AC with an Evaporator Cooler at the sametime. One pulls moisture out of the air, the other puts it in. They are two different types of cooling. If you didn't know that, I don't think you know enough about evaporator cooling in general and how it works. This is not a hit on you. This is one of the things I was talking about in my original post.

      I did some research, and found the power uses for the three main cooling types that are all equivalently to a 3.5 ton AC to run for 12 hours a day with a cost of electricity of $0.115 for 30 days:

      3.5 ton AC - 4500 watts an hour - $186.30
      Mini-split with an EER of 15 - 2700 watts an hour - $111.78
      Evaporative Cooler - 456 watts an hour - $18.88

      Assuming each last for 10 years (does not take into account the maintenance costs) and is run for four months a year:

      The cost is very large. I will note that the EC uses 2.5 gallons of water an hour that is not included in the cost. There is an interesting article I found that talked about that too. The amount of water that is used to generate the electricity, is higher than with the EC would use.

  2. Expert Member
    BILL WICHERS | | #5

    "Regular" evaporative coolers only really work in areas of persistant low humidity, like Denver. Areas with higher average humidity levels will see little benefit from an evaporative cooler, and the evaporative cooler may actually make things worse. Evaporative coolers also need crossflow, not a sealed space like air conditioners need, so you need to design the house to work with them (at least the ventilating system).

    You can't really use an evaporative cooler together with an air conditioner, either, because the higher humidity levels produced by the evaporative cooler will reduce the efficiency of the air conditioner in lowering the air temperature due to the need for latent heat removal (dehumidification, basically). You could put in both systems, but you need to run either one OR the other, depending on conditions.

    If you're in an area of low average humidity levels, an evaporative cooler is a GREAT way to cool -- very energy efficient. I think Xcel Energy in the Denver area even offers some incentives for people to install these units. In very large facilities, we often use "cooling towers", which are like evaporative coolers, but for water instead of air (think of a water tower as a waterfall in a box with a BIG fan pulling air through the waterfall). These work because evaporation of some of the water acts to lower the water temperature, which means the water coming back from the cooling tower can actually be below the outdoor ambient air temperature. This is a big efficiency gain for large chiller water systems that are commonly used to cool shopping malls, big office buildings, and large datacenter facilities (which is what I work with, primarily). The downside is that the performance of cooling towers varies with humidity levels just like evaporative coolers do, except that since the cooling towers aren't directly cooling the air in the space, it doesn't matter if humidity levels of the exhaust air get up to 99%. The other downside is that you have large amounts of makeup water required, which means you're trading water for electricity in terms of "energy" use, basically. This can be a problem in areas where water is scarce and/or expensive, and that same tradeoff applies to evaporative coolers used on homes.

    I suppose the short answer to the OPs question is "yes, evaporative coolers can, and probably should, be considered, but only in areas where they make sense due to low average humidity levels". A secondary consideration would be water use -- if you're in an area of severe water shortage, like many places in the West are, that's another concern in addition to energy use and the water vs energy consumption tradeoff should be considered if you are trying to build green. There is no free lunch in the world of physics, unfortunately...


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