Seeking Engineer for Off-Grid Religious Facility Heating in the Mountain States

jesmed1

@DCContrarian Yes, that's a lot of air. But again, it's a tradeoff. Would you rather have giant fans running, or giant compressors? If the architect isn't lying, the fans apparently do cost less to run than AC compressors.

Also, he did say the thermal exchange between the thermal mass of the building and the airflow was an important part of the design. Air sucked through the building at night cools the concrete "teeth" in the air passages, and the following day, the cooled concrete teeth cool the warmer daytime air being sucked in. He says the daytime air gets cooled by 3 deg C as it flows through the passages, and that the fans slow to 2 ACH during the day, presumably to give the incoming air more time to lose its heat to the concrete teeth.

DCContrarian

@jesmed1: "I will say that if I were the clients building a $30M building in Africa with no air conditioning, I would insist on a significant engineering effort to prove that my building was not going to become an uninhabitable greenhouse, and I expect the clients were smarter than I am."

Nowhere does it say there is no AC, just that it uses 35% less energy than full AC.

"Either way, when you look at the cross-section and see the way natural convection is used for both ventilation and temperature regulation, obviously a lot of careful thought and planning went into it. "

It's not using natural convection. It has 32 banks of fans doing ten air changes per hour.

jesmed1

@DCContrarian I can't go to Zimbabwe at the moment and inspect Eastgate to satisfy myself that there are no hidden air conditioners, so you're free to draw your own conclusions. But the Arup Engineering webpage says there is no AC.

And yes, I would call it "mechanically-aided" convection. The central stack design will assist with some natural chimney effect. It seems there may be some times when even the fans don't run, which is what I assume they call "passive" ventilation, during which they say the building uses only 10% of the HVAC energy of a comparable building.

Here are some more links with more details about the cooling system:

https://www.arup.com/projects/eastgate/

https://en.wikipedia.org/wiki/Eastgate_Centre%2C_Harare

Also, this NY Times article says there is no AC:

"Mick Pearce of thePearce Partnership was given a challenge by Old Mutual, an insurance and real estate conglomerate: build an office block that would be livable with no air-conditioning and almost no heating.
Eastgate, the result, has been open for only nine months, but so far Mr. Pearce seems to be succeeding: the complex has been using less than 10 percent of the energy of a conventional building its size. Old Mutual saved $3.5 million on a $36 million building because an air-conditioning plant didn't have to be imported."

DCContrarian

Harare, Zimbabwe is a very mild climate. Here's a chart:

I use the term "shoulder season" to describe days when the high is above room temperature and the low is below room temperature, most buildings won't need either heating or cooling in shoulder season. Their whole year is shoulder season!

jesmed1

Yes, that design approach was only possible because of the mild climate. The architect said as much in the NY Times article:

"This is all possible only because Harare is 5,400 feet above sea level, has cloudlessskies, little humidity and wide temperature swings -- days as warm as 88 degreescommonly drop to 58 degrees at night.
''You couldn't do this in New York, with its fantastically hot summers and fantastically cold winters,'' Mr. Pearce said."

Obviously a termite-mound-inspired building is not going to work in the Rocky Mountain climate. I only mentioned Eastgate as an example of a building that had actual design engineering done up-front on its thermal mass, as illustrated for example by the heat exchange between the ventilation air and the concrete "teeth" in the air passages.

The point being that actual engineering analysis and design of thermal mass can be done if the client is willing to spend the money for thermal modeling, as opposed to just pouring thick slab floors or walls, calling it thermal mass, and hoping something good happens. But obviously the actual design and how best to use thermal mass is going to be influenced heavily by the local climate.

Maybe in this case, the best thermal mass is just a giant buffer tank that absorbs BTU's from the wood boiler during the day and releases those BTU's slowly overnight by circulation through slabs or radiators. Then the engineering can be as simple as calculating how many BTU's will be stored in the buffer tank, calculating the release rate of those BTU's by circulation overnight, and modeling the expected interior temperature over a range of overnight outdoor air temperatures.