No HVAC wall/roof assembly in hot/humid Climate Zone 1A
We’re building a home in zone 1A Honoulu, Hawaii. It’s a year round cooling climate with high humidity. The house is on a steep site, and currently planned to be built on piers with airflow underneath, 2×4 walls, and a vaulted ceiling. We do not plan to have any type of AC. The main source of cooling will be through trade winds and ceiling fans. Outdoor air quality is high. Humidity is a bit of a challenge, but with an open, cross-ventilated house it’s just something to live with.
From October through May, the house can be fully open and we’ll aim to match the outside temperature. From June through September, we’ll want to delay the heat gain until the evening when we can flush the house through ventilation/the use of lightweight materials that release heat as quickly as possible. I’m thinking that’ll look like closing the house in the morning and opening it back up towards the evening, provided that we can keep a most of the daily solar gain out of the house.
What would be the recommended wall/roof system for this? Is there a way to use radiant barriers effectively or should I just use a reflective roof? Is there a best type of insulation for this system? Trying to do this in a cost effective way, but open to all ideas. Any other thoughts are welcome.
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If you are going to go without AC and open/close, then it's better to go with a high mass interior. Preferably with fans to assist in moving air through the house at night. In any case, also use ceiling fans.
Why is that? My understanding is that mass will regulate the interior temp, basically averaging out the highs and lows. Cooling in the day is welcome but heating at night is definitely not.
If you don't have enough mass you will reach thermal equilibrium too early in the day as your mass saturates with heat and run hotter.
"average out" is also a myth. The average temp of the thermal mass depends on the transfer rate - which you can control.
Move enough air as soon as the outdoor temp drops and the walls being warmer has almost no effect.
I've tried it all in a very hot climate and open/close was better than nothing. Much better would have been solar panels, an air->water heat pump and a water storage tank.
That makes sense in regards to the mass. Can you explain more about how to use a heat pump and water tank? I'm trying to research it, but not finding much. Thanks
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Nate,
Hawaii is a pretty good state for solar since electricity rates are so high. Have you looked into it? (https://www.solarpowerrocks.com/hawaii/) Solar plus a Sanden or even a more conventional split mini HVAC system would be efficient and make for a more comfortable home.