Manual 11196906

Manual 11196906
20929 Bridge Street, Southfield, MI 48033
4121 Brockton Drive SE, Grand Rapids, MI 49512
6200 Baron Drive, Bridgeport, MI 48722
6910 Treeline Drive, Suite A, Brecksville, OH 44141
Phone: (800) 589-6120 - Fax: (248) 354-3710
www.deppmann.com
Serving the industry since 1927
August 31, 2009 ~ Monday Morning Minutes:
High ΔT Hydronic Heating Systems (Part 3)
Last week, we used an AHU unit system example which showed the advantages of reducing the
return water temperature at design, as well as, raising the delta T. The AHU unit example ended
up with 1,700,000 BTUH with 85 GPM from 160°F to 120°F. Today, we will continue to look
at terminal units, with the goal of increasing the delta T and lowering the return water
temperature for the other terminal types in our example system.
The balance of the terminal types, in our example are: reheat coils, fin tube, ceiling radiant and
floor radiant systems. Let’s assume in this example the loads respectively are 800,000, 350,000,
300,000, and 300,000 BTUH. Including the AHU system, the total BTUH is 3,450,000. If we
used a 180°F EWT with a 20°F ΔT, the secondary system pump would have to be 345 GPM
using 5” or 6” pipe.
Reheat coil selections normally require the leaving air side temperature below 90°F with limits
on the fins per inch of the coil.* Changing to a 150°F supply with a 120°F return, takes some
additional selection time, but will result in a more efficient hydronic system.
Fin-tube selections, with velocities below 3 FPS, require more fins per inch which is relatively
inexpensive. As long as we keep a reasonable average temperature, changing the ΔT will work
fine. In our example, we could change to 170°F supply with a 120°F, giving us an average tube
temperature of 150°F.
With ceiling radiation we pay a huge sizing and cost premium when we change the average
temperature, so we will keep it at 180°F supply and 160°F return.
The floor radiant system is designed to take lower temperatures and would require a mixing
valve, if we supply 180°F, so we will use a design of 120°F to 100°F.
Let’s change the temperatures and see what type of boiler ΔT we can achieve. The following
table summarizes our design. (I rounded to the nearest whole number on the chart)
BEFORE
Zone Name BTUH Secondary EWT Secondary LTW GPM Secondary AHU Units 1,700,000 180 160 170 Fin Tube 350,000 180 160 35 Reheat coils 800,000 180 160 80 Radiant Floor 200,000 120 100 20 Ceiling Radiant 400,000 180 160 40 Total 3,450,000 180 160 345 Continued on page 2…
Disclaimer: R. L. Deppmann and it’s affiliates can not be held liable for issues caused by use of the information on this page. While the information comes from many
years of experience and can be a valuable tool, it may not take into account special circumstances in your system and we therefore can not take responsibility for actions
that result from this information. Please feel free to contact us if you do have any questions.
20929 Bridge Street, Southfield, MI 48033
4121 Brockton Drive SE, Grand Rapids, MI 49512
6200 Baron Drive, Bridgeport, MI 48722
6910 Treeline Drive, Suite A, Brecksville, OH 44141
Phone: (800) 589-6120 - Fax: (248) 354-3710
www.deppmann.com
Serving the industry since 1927
August 31, 2009 ~ Monday Morning Minutes:
High ΔT Hydronic Heating Systems (Part 3) – Continued…
AFTER
Secondary EWT Secondary LTW GPM Secondary Primary EWT Primary LWT Primary GPM 1,700,000 160 120 85 180 120 57 Fin Tube 350,000 170 120 14 180 120 12 Reheat coils 800,000 150 130 80 180 130 32 Radiant Floor 300,000 120 100 30 180 100 8 300,000 180 160 30 180 160 30 239 180 130 139 Zone Name BTUH AHU Units Ceiling Radiant Total 3,450,000 What have we gained? The load obviously remains the same, but the flow rates are lower and we can use smaller pipe sizes, smaller
pumps, and lower horsepower. The return water temperature is 130°F, at design, so we are taking advantage of our condensing boilers
at design. When we apply the reset schedule to this system, the efficiency will be even greater.
Next week let’s take this example and design the primary secondary bridges.
Thank you for using products sold by
R. L. Deppmann Company in Michigan and Ohio!
Disclaimer: R. L. Deppmann and it’s affiliates can not be held liable for issues caused by use of the information on this page. While the information comes from many
years of experience and can be a valuable tool, it may not take into account special circumstances in your system and we therefore can not take responsibility for actions
that result from this information. Please feel free to contact us if you do have any questions.
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