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7/7/14

Off Grid Passive Solar Prefab House Muses On HRVs Air Conditioning And The Bay Breeze

There is a potential modern prefab house project in Florida I have been working on, and in answering some general questions about structural insulated panels, I ran across this general SIP tips post I thought others might find useful. If you are a contractor or client interested in a general "overview" on some points to think of when working with SIP, it has a lot of great points to consider, from finishing to window framing, and more.

I tidied the prefab house a bit this week, and as I did, I noticed again how, in summer, diffused light fills the modern prefab house, yet it doesn't heat.


But my, in these southern summers, it can get hot...
Dog days o' summer.

In our off grid passive solar SIP house, we open windows at night, then close them to trap in the cool air in the morning. Our clerestory windows release hot air, risen to the roof. But some weeks it doesn't quite cool at night, with searing temps in the daytime!

Dog days o' summer, with chicken.
And solar cooker in the background.
On some summer days in the south, the clerestory windows, the passive solar design, the insulated SIP, the fans, the cross-ventilation, the shady overhangs, the cold spray bottle of water kept in the fridge to mist the air and body for refreshment, the hammock under the oaks... is still not enough to cool down.  I don't blame people in the south if they don't want a little something more to take the edge off. 

I mean, the heat index DID get up to 110 this week...!

Coupled with an ERV or HRV, a minimal air conditioning solution is understandable.
We have an HRV. Here is a good overview on how, with a passive house, an HRV can provide fresh air in a tight envelope.  But what about air COOLING?
From EcoBuilding, some details on a Passive House project and why they chose a particular HRV:
"We found HRVs on the market, but most of them recovered little more than 60 to 70% of the heat in the air.  Many of them used so much electricity for their fan motors that they used more energy than they recovered. We learned that there are several brands of HRVs sold in Europe that combine low electrical consumption with high heat recovery.  In fact, the Passivhaus Institut certifies only HRVs that recover at least 75% of the heat in the exhaust air (with low electrical consumption).  
When people think of heat recovery ventilators (HRV), they typically only consider winter operation because HRVs’ better-known winter utility (heat recovery). However, in summer the HRV 'works in reverse.' On the hottest summer days, the HRV becomes a heat rejection ventilator. 
In warm days, we sometimes turn our HRV to the lowest setting since we have free ventilation from open doors and windows. However, on the hottest summer days, our HRV ventilation system provides comfort without air conditioning. Our HRV system flushes warm stale air out of our house at night with cool air from outdoor. Then, during the heat of the day, as the outdoor air temperature may rise to 90F or hotter, our HRV transfers the heat in the incoming fresh air to the outgoing stale air, acting as a 'heat rejection ventilator.' We hardly use the ceiling fans we installed in 1998."
Here are more links I found interesting:
While I start to research more about an actual small air conditioner, which is tedious and boring, the heat rose and we changed locations (again), heading for water, wind, and sail...
Onward to the Chesapeake Bay and the 150 year old In-Town Ramshackle!

Oh the excitement of July 4th... with Miz P from NYC!
With Miz P in front of The RaaaaaaaamSHACKLE, y'all.

When it's hot, southerners eat a lot of cold food.
Gazpacho, cucumber sandwiches, cold pasta salad...

When it's hot, southerners hit the water.

C. showing P. her boat, from Norway -> NY -> DVL!
 
And then there was the 4th of July!
We had a lovely, intimate dinner with The H's, when, to our delight, down the point, someone staged a fireworks show that was hard to beat. We viewed from the deck, overlooking the creek, cheering as huge fireworks burst over the back yard, while the children ran in circles, sparklers wildly sparking.
And, true to our herd, Miz P commandeered a boat!
 
What will this week bring at the modern prefab house -or- the In-Town Ramshackle? I don't know. But I aim to enjoy every second of the summer.

Hydrangea pom-poms.
 

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