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HVAC systems

Matthew Hicks | Posted in Mechanicals on

Hi all,

Last week I asked my first question about how to improve my building envelope and reduce mech system costs. using coolcalc.com, I simulated a number of manual J scenarios, I think I have the envelope options down to 1-3 things and will await results from my energy consultant.

The question now remains as to how to best heat & cool my home. On that post, many people suggested Chilltrix, but one poster suggested Implementation risk. They didn’t really explain what they meant by that.

With that said, when I try to estimate how much I would save by putting in a heat pump system like Chilltrix in compared to my HVAC guy’s current suggestion of a 96.5 multi stage forced air furance and a 17 SEER multi stage condenser….. the numbers don’t really suggest much savings, particularly because I am in zone 5 and could potentially need back up heat during cold days.

perhaps it’s a cost of energy thing – delivered cost of gas is $7.75-$8.00/MCF the past few months, and the cost of electricity is $.23/kWh.

What am I missing here? Why was everyone so focused on the mechanics of my house over insulation?

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Matthew,
    Q. "Why was everyone so focused on the mechanics of my house over insulation?"

    A. I'm not sure who "everyone" is. Here at GBA, we always advise that it makes more sense to invest in an excellent thermal envelope -- one with high levels of insulation, low levels of air leakage, and high-performance windows -- before investing in an expensive mechanical system.

    -- Martin Holladay

  2. User avatar GBA Editor
    Martin Holladay | | #2

    Matthew,
    Q. "Many people suggested Chiltrix, but one poster suggested Implementation risk. They didn't really explain what they meant by that."

    A. I assume the person who wrote that comment meant that implementing the suggestion to install a Chiltrix unit is risky, because it's hard to tell if your installer knows what he or she is doing. A Chiltrix system needs to be designed, and there aren't many residential HVAC installers who know anything about designing a hydronic cooling system that distributes chilled water.

    For more information on Chiltrix systems, see Air-to-Water Heat Pumps.

    -- Martin Holladay

  3. Andrew Bater | | #3

    Matthew, this is the part of your original question that made me think that water (Chiltrix or other) could be a natural solution:

    "As such, we only have one wall to run ductwork and plumbing up and very little wall space to insulate. The HVAC sub has advised that we will need two furnaces and condensers with the 2nd set being on the third floor due to the lack of wall space (we have no interior walls that run up all three floors and we plan to have 6 zones in the house (lots of duct work)"

    Participants on this forum all look at questions/discussions based on their own experience/biases/etc. In my case, having commercial experience with mechanical systems that use steam, hot water, condenser water and chilled water, that is just what I gravitate to. Or maybe I should say "flow" to.

    As I followed your thread after my comment, I saw that you had received suggestions for insulation, and that mini-split units or a derivation of same had also been suggested for HVAC. That seems to be the normal progression on GBA, and I think probably rightly so.

    Water is a superb way to move heat around. Unfortunately it's generally not cheap and it's generally not simple. It's not for the faint of heart. However at a certain stage structures become too big, too tall, too complicated, or there is too much heat to provide or extract. At that juncture ductwork becomes difficult or impractical and water turns into a better solution. You could be at that tipping point. However if you aren't comfortable with it, or your contractor isn't comfortable with it, or your construction budget isn't comfortable with it, well then I would go a different direction.

    BTW, I am not that far from you. You and your wife are more than welcome to take a ride up here to see a water based HVAC system, one that the design thereof was actually driven by aesthetics and lack of vertical aperture for ductwork.

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