Hydro air reset curve

Wayco Wayne_2

for the replys guys. This was one of the rare instances I didn't do a heat loss. The house wasn't that old. Mayby 10 years. The customers had a nightmare Polaris experience so they wanted it gone. The Polaris was rated at 100,000 btu's. I am installing a new Prestige boiler that is rated at 110,000. It has a built in outdoor reset so I wanted to use it to it's full advantage and mayby even get below 140 degrees for some of the curve. I will probably use Dave's suggestion to measure outlet air temp and make adjustments. Also might use Constantines suggestion to show customer how to adjust the curve up and down, though it's sometimes risky letting the customer fuss with the controls. :o WW

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Wayco Wayne_2

I am working on a system that

has hot water coils in the air ducts. The system has outdoor reset. I'm sure I can save them some money by utilyzing the OA control. Since the coils were pre-existing I can only guess at thier capacity. How low can you go? thanks for any input. WW

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GW

idea

That's a challenge. You may want to do a heat loss, throw a dart at the wall on insulation and infiltration and glass U-value, and size the new boiler to hanlde the output required at this day regardless of what's in the ducts now.

That's what I love about the industry we so love: People honk and toot there horns that a heat loss must be done, but several key factors are just a guess anyways!

Also, and perhaps most imprtantly, duct systems can be anywhere from complete junk to OK; rarley will you or I come across a top quality duct system.

So, if the duct system is lame, how do you adjust for that? Wrightsoft has a field where you can input the duct quality (sealed/unsealed? Insulated with what R-value? Duct location? Attic temp?) and the furnace/boiler size would be affected.

Gary

Constantin

I'm with Gary...

... do a heat loss, measure the air speed, then determine what the temperature of the air has to be coming out of the coil to match that heat loss. Geoff recently published the formula for airflow, temp, and BTUs, so that should give you the maximum temp needed to keep these coils happy.

"The basic formula is CFM x ΔT_air x 1.08 = Btuh"

Then educate the customer on how to set the curve and adjust it as necessary on the coldest of days if it cannot keep up.

Dave Yates (PAH)

well

I'd go for the outdoor reset and given the steady-state return air value, I'd adjust the delivery temp downwards until you see the lowest air delivery temp you customer will feel is warm - probably about 115 at the register face.

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