Design Challenge

Wayco Wayne_2

I'm friends with is building a meeting house. It's a pre-fab house kit for a structure called a Yurt. (It's patterned after tent like structures made by the Mongols years ago.) It's floor is a 34 ft in diameter circle. The Walls are 10 high and the ceiling is cathedral ending up in a 6 foot skylight in the middle, which can be opened. I thought radiant floor right away, since the floor is going to be a concrete slab, but since it is a commercial building it has ventilation requirements that complicate matters. The Yurt is designed to ventilate through it's 11 windows (13 sq ft each) and up through the skylight with a natural chimney effect, but the County is saying it needs mechanical ventilation which adds up to 1200 cfm (15 cfm per person, full capacity of building is 80 people) They like the radiant floor idea but feel they are being forced towards forced air which won't be easy because there's no place for ducts. I was thinking ductless for the A/C would work. Does anyone have any suggestions. I'm a residential contractor and don't know my way around these ventilation issues very well. WW

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Wayco Wayne_2

Just thinking some

more on this. If I used a furnace that brought in 100% fresh air and figured for a 50 degree delta T it would require 65,000 btu's just for the fresh air. The heat loss for the space alone is 36,000. This fresh air is a killer. WW

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GMcD

Natural ventilation

A yurt structure is ventilated by natural ventilation, and based on the bouyant air plume generated by 80 people, there ought to be enough air moved to provide healthy ventilation at any time. Trouble is, you need a computation fluid dynamics computer model to prove it to the satisfaction of your "authorities". I would suggest that you first try to find a local consulting mechanical engineer that could do the natural ventilation model, and failing that, the "simple" solution would be to throw in a couple 600 cfm air to air heat recovery units, and use those with your radiant floor slab. The peak lowest winter temperature being supplied to the space from the heat recovery units might be as low as 50-55F, but with the heat load created by 80 bodies and the "resultant temperature" created by the radiant heat, the space should be quite comfortable without supplemental heat on the supply air from the HEX units. You could always use a couple of warm water reheat coils piped with the radiant slab water to touch up the supply air if needed. Consider operating the HEX units with a CO2 sensor for demand based ventilation. I'd bet the HEX units won't even come on anyway if there is enough natural ventilation present.

Wayco Wayne_2

Thanks for the input Geoff

I agree with you that the natural ventilation should be enough. I have seen residential heat exchangers for fresh air but they only go up to 200 CFM. Where do I look for 600 cfm HEX's? WW

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Murph'_4

how about

getting the name of the "yurt" companie and see what they suggest, why re-invent the wheel or "yurt"



Murph'

GMcD

Venmar heat recovery units

Venmar makes air to air HEX units in many sizes up to big commercial applications- weblink: http://www.venmarces.com/home.php?body=unitary&menu1=1&menu2=1

Lifebreath also makes some but only up to 265 CFM according to their website. There are other types of commercial HEX units that pop up on a web search.

Another commercial style plate HEX unit is the Fantech, weblink: http://www.fantech.net/khp10000.pdf for a nominal 600-700 CFM unit.

Stay away from the rotary heat wheel type units and look for the passive plate type HEX units.

Wayco Wayne_2

Hey Murph

I thought of calling them first thing, but apparently they are hands off as far as things mechanical. I don't know why. Maybe afraid of litigation or just don't want to get caught up in any problems. Seems to me they are missing out on an opportunity to have some pre-made solutions. $$$ca-ching. WW

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Wayco Wayne_2

I looked up

Venmar's website. Looks like it would work just fine. Although I'd rather get the natural ventilation approved. Thanks for your help. WW

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