Opinions please on controls for HW coil AH's....Boilerpro

Boilerpro

Looking at 6 air handlers that currently have modulating valves for steam coils. System is being converted to Hot water. 4 AH's are used for ventilation air only, 2 for ventilation and heating. Need a way of modulating heat output of coils for ventilation and then boosting output for heating for quick recovery from setbacks. Been thinking variable speed pumping into a continous pumped loop through the coil from a continuously pumped loop from the boiler room. The boiler loop is also going to be fully reset, depending on feedback from indoor sensors on various zones. However, at my tekmar classes, I was told that the injection controls don't work too well with air handlers, probably due to too rapid of air temp changes.

One more unrelated item. I hope to start installing the ductwork for central air in my home. It is going in the attic and I plan on using round pipe since it can handle more air flow with less exposed area. However, I haven't seen any really heavily insulated duct systems.....with 110F attic, 55F cooling air I wanta to keep the system losses to a minimum. Any suggestions? ( Hi velocity systems probably not a good idea since no one in this area has ever worked with one).

Boilerpro

ed wallace

a/c ducts

good idea about useing round duct what you need to do is get a roll of isulation and insulated the ductwork that way you will no have a problem with condensation in or on the ducts

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Art Pittaway_2

Hi Chief!

Insulation is available in sleeves, like flex duct without the lining, pull it on and tape the joint. Control'd had it and other jobbers probably do to. Ask Chuck at Yeoman's he'll know.
The water coils, will there be a chance of freezing? Whenever I see or design a hookup that may freeze I use a dedicated pump on the coil to give constant flow and usually a 3-way to modulate the coil output temp. The 3-way should be spring open to the coil so it will over heat rather than freeze. Customers are unhappy when they are to warm but get downrite testy about broken coils in mid winter. This project may be more than a tekmar can handle, I assume it's a good size commercial building, is H'well, B/C or Johnson involved? The central management system might be worth a look. See ya at the gathering! Art

[Deleted User]

round insulated ducting,

like the type supplied with my high- velocity system, might be the answer. They are 9 in.I/D, sort of a spun fiberglass with a vapor barrier wrapper. Similar to duct board only round. I think it is a Johns-Manville product.The ones i have here come in six foot lenghts.

Michael B

controls, space-pak

I have been in contact with a company called Calefi (rep. Mike Dore out of Chicago) that has a really slick control (see attatched). They may be able to help.

It sounds like high-velocity system is the way to go. I understand that it is not that common around your area but so what. They are easy to install, they fit the design critera and they deliver copus amounts of cold air.

RB_2

Valve size and characteristics are crucial for stable control.

If you provide the capacity of each coil, include the design parameters ie: entering fluid and air temperature at maximum load, design fluid delta t, fluid pressure loss through each coil at design flow, proximity of the valve to the coil, the coils intended purpose, available control power, and whether you need a discharge air control as part of the proposal...and I'll throw together the schematics and parts list and point you in the direction of where to purchase the stuff.

For our HVAC valves and actuators for air handlers copy and paste this link:

http://bc.danfoss.com/PCMFiles/1/Master_hvac/hvac_products.asp?MenuUID=1AA0C152-432C-4BAA-B2D8-74CDA46B1466&MenuID=24

For HVAC controllers for ventilation and air handlers copy and paste this link:

http://bc.danfoss.com/PCM/Presentation/ProductType.asp?DepartmentID=1&LanguageID=1&ProductgroupsID=33&TypePID=1668&MenuUID=D57A77DF-BB23-49BF-97A4-B5E5B0AABAC7&MenuID=1

For the downloadable smart software card, which gets married to the controller, copy and paste, this link...look for the C14 Card.

http://bc.danfoss.com/PCM/Presentation/ProductType.asp?DepartmentID=1&LanguageID=1&Show=&ProductGroupsID=30&TypePID=1642&TypeID=378

I'll be back at work on Monday...you are always welcome to call me at 403.236.9560

Regards,
RB

Aidan (UK)

AHUs

I wouldn’t use boiler reset. The AHUs will require a higher flow temperature than the indoor heat emitters. Boiler re-set would only be practical if you have a DDC /BMS control system which can increase the boiler flow temperature in response to the minimum water temperature required by the AHUs AND the indoor heat emitters.

I would suggest that you supply the AHU’s from a constant temperature (CT) zone pumped directly off the primary loop and supply the indoor heat emitters from a second, modulating temperature (MT)/outdoor re-set loop via a mixing valve.

See

http://www.pmengineer.com/pme/cda/articleinformation/features/bnp__features__item/0,2732,21624,00.html

about mixing reset.

Each AHU heater coil should have an isolating valve on the flow and a regulating valve/circuit setter on the return; this should have a flow-measuring device to allow the system to be proportionally balanced.

The control valves Cv should be selected according to the coils’ resistance, they’re usually smaller than the line size. UK practice was to use 3-port control valves; there would be a second regulating valve on the by-pass leg. This arrangement has the great advantage of giving a constant hydraulic resistance, and so a constant flow-rate, regardless of the position of the control valve.

A 2-port valve would reduce the total flow rate as it closed, increasing the pump’s differential pressure and the flow-rate through all the other heater coils, and so increase their heat outputs. Two-port valves are now often used in conjunction with speed-controlled pumps, which maintain a constant differential pressure despite variations in the flow-rates.

I’d use a capillary-type manual-reset thermostat, downstream of the heater coil, to stop it freezing. The thermostat is hard-wired to the fan motor’s contactor, so that the fan is stopped and the inlet damper closed, if the coil’s air-off temperature approaches freezing.