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Old 05-08-14, 02:45 PM   #111
buffalobillpatrick
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ODR is not perfect, it does not take into account several things:

Wind & thus infiltration, and clear cold night radiation into space.

I have designed & tested an Outdoor sensor that takes both factors into account.

It consists of a small slightly heated steel box, like a very very small house.

It reacts to wind & night radiation in that both cause cooling below air temperature.

It's normal temperature is 10* F above ambient, so this must be adjusted for when setting up ODR parameters.


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Old 05-08-14, 02:55 PM   #112
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NiHaoMike,

"Even better is to only raise the tank temperature using the heat pump if it's not keeping up with demand. "

A heat source not keeping up with demand, is an issue that I haven't worked out yet.

Kind of like, when to down shift going up a hill.

I could do a time delay & check status to determine if gaining or loosing ground.

Sources of info such as:

http://www.geoexchange.org/forum

Recommend 2 tanks with desuperheater.

I believe that buffering is necessary between heat source & sink.

My 2 ton HP will, in all cases, output more heat than any 1 or 2 hydronic zones require.

Some buffering will take place in slab floors, but unlike some French systems I've read about, I don't want to overshoot room thermostat for a bit of eff.

I have some nice PID Tekmar thermostats that have a air sensor & a slab sensor to help prevent over & under shoot.

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Old 05-08-14, 03:57 PM   #113
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You could measure the derivative of the space temperature and see if it's going up or down. It would probably be necessary to do some filtering to prevent noise from causing false triggering.
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Old 05-08-14, 06:02 PM   #114
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Trying to chase room(s) air stats with buffer tank temp. Would cause big over/undershoot.
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Old 05-08-14, 06:48 PM   #115
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As I've designed it, as soon as the heat pump starts up, the heat output is immediately used for the floor heating (with the remainder going into the tank) so the response is almost instant. The floors are going to have a lot of thermal mass (much higher than the room air in a more common air type heat pump) and the system would have a lot of time to respond.

If you're trying to get very precise temperature regulation, you'll likely need to use a VFD. But I'm pretty certain it would work more than good enough without one.

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