unico hot water coils

clammy

I have checked out what is avaiable from unico as for hw coils for a possible hydro air system but my conserns are that i would like to use a coil that would work a little better being the boiler side is going to be a htp munchkin m80 but i would like to use a coil that is rated at 80 btu output but at a much lower water temp on design day looking for 80 mbtu at entering water temp of 140 or so the a/h is the 3642 blower with the 3 1/2 coil it will be heating and cooling 3 levels of this home .As for the heating and cooling system now well it does not work due to the fact that all main trunk in the basement was removed and miles of flex where run ,the returns are well below mimuin for a 3 ton a/c and the heat only brings the home to about 60 degrees on 20 degree days the furnace is sized correctly it's just the duct work is history and as always they want no baseboard no radiant no visiable duct work anby wherer i guess they need a magicain instead of a mech thanks for any info peace and good luck clammy

Brad White

Hey Clammy

Glad to be seeing your name more frequently.

I wonder if you could replace the coil with a deeper one, even custom, such as made by Heatcraft or TSI if the Unico coil itself is not cutting it. What is the current coil rating versus heat loss at your presumed CFM?


If you have "x" depth in direction of airflow you might get a coil with a density in fins per inch but more importantly number of rows to get the heat you want. Interlaced circuits also give better performance than the less expensive serpentine coils. Measure the coil absolute dimensions and check them out. First Company and McQuay also makes custom coils among others.

Select the coil for 130 degree average water or less and see what you come up with. Your coil may well be 3 or 4 rows deep and that would fit into a 5-inch deep casing.

If this does not fit into a unit then a second coil ducted in series (and piped in parallel per the posting below) may be needed. You do have options but a challenge to anyone's fitting abilities.

Do you have an idea of what airflow you actually are moving? That too is necessary to know within a range at least.

One other thing: Counterflow. Make sure that the hottest water (the supply obviously) enters the coil to serve the leaving rows first. This gives the best send-off to the air coming off the coil. It also promotes condensing as the cooler return water sees the coolest entering air.

Good Luck!

Brad

Bruce Stevens

Brad

I know you know the answer so I'll ask the question, would it be better to run the water piping to two sets of coils parallel or in series, if stacked one in front of the other?

Brad White

Always interesting...

I would run two coils piped in parallel, Bruce, and stage them. The first coil would do what it can do in mild weather and the second one would fill in as a second stage and would see hotter water rather than the "return from the first coil". I think that this would give the best control.

On some performing arts centers I have designed, I would have a HW preheat coil upstream of the cooling coil and after that, a reheat coil for humidity control. Naturally the HW coils were piped in parallel so that the reheat could work with it's minimum tight controlling GPM after the cooling coil has done it's work.

What I found was that in winter time, when a larger amount of outside air is needed (over 50% outside air sometimes) and a fast warm-up is required, it gives a nice boost.

One could argue that if the coils were piped in series the leaving water would be cooler going back to the boiler. I would counter that by saying that at least with two coils you can control it more tightly.

Going in though there are first costs to consider- If I were not using reheat as a dehumidification strategy on the theatres I was designing, I would not have entertained the secondary benefit.

Does that make sense?

Ted_9

unico

Unico has charts on using lower water temps. Off the top of my head I think it shows 160 supply temp water and 140. I did two with out door reset boiler and they heat the home just fine. I believe the Unico coils are deeper thats why you can use lower water temps.



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clammy

Thanks to all

Thanks for the info unfortunatly i have lost my unico binder some where with my normal paper trail but i'll find it or get another one i some times don't like reading it from a computer screen old fashion,as for cfm,s only looking at about700 cfm 3 1/2 ton a/c and in all probalblity only a single stage coil set up and brad thanks for that coil reminder would have remenbered before piping in the past saw alot of those old computer room systems you know outside reheat ,re cooling re heat ,humidifer old stuff this is simple but with some wild duct work kicking every where and of course house like a meausean with alot of nick nack .iwas really looking for a inlet temp of 140 max on design day hopefully i'll get a binder tommorow from my trane guy peace and good luck clammy

Bruce Stevens

I like your thoughts

and especially making it a two stage system on the coils, that would put the icing on the cake for me. I was just thinking about the cooler return temps with series, not that I would have thought it best in my minds eye.

Ted_9

Unico coils

This is from the Unico book.


HW-3660


700 cfm, 140 degree entering water temp.

4 gpm= 45,100 btu's

6 gpm= 48,800

8 gpm= 49,500

10 gpm= 45,100(that may be a misprint)



BTW, here are some nice hand books from my friends a Capco Supply:

http://www.capcosupply.com/unico_handbook.htm








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Brad White

Which all illustrates why

more flow, even doubling it, has a relatively small effect on output.

Temperature is everything and by doubling your flow on a 20 degree delta-T system you have raised your mean water temperature by five degrees.

By the way, at that airflow and 4 GPM you would get a 59 degree rise on the air side, entering at say 70F and leaving at 129F. That is about as high as I would go, myself but it all depends on your heat loss. I like to run my air as cool as possible but at least the 100-110F range so it does not feel too cool by the time it gets to the skin.

clammy

Thanks Ted

ted thanks for the 2 attachements ,they got me looking and thinking that as always this job will be a tough one and i guess there's gonna be some second stage heat in a few areas thanks again peace and good luck clammy