Len Phillips
What percent of loss (line loss) should I expect to see in a large district heating distribution steam system of about 400 customers, mostly heating with some hot water, located in the Midwest?
Hendrik Shank
In Rochester we have a superheated steam system with about 47 customers and approximately 9 miles of pipe. We average around 40% line loss.
Hendrik Shank
Mechanical Engineer
Rochester District Heating Cooperative
150 State Street, Suite 110
Rochester, NY 14614
(O): 585-546-8890
(C): 585-353-0399
(F): 585-546-6570
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David Christiansen
The following is posted on behalf of IDEA member Jack Powers of WE-Energies, Milwaukee, Wis., jack....@we-energies.com:
What percent of loss (line loss) should I expect to see in a large district heating distribution steam system of about 400 customers, mostly heating with some hot water, located in the Midwest?
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Phelps, Tom
Jack,
There are many factors which influence the losses for district energy steam distribution systems. When the variability in all of these are considered, it is more understandable why there are wide variations in estimates of line losses between different operating systems.
Accounting Influences:
1) Steam production is usually metered at each boiler’s outlet, but “inside the plant” steam use and heat loss are rarely metered and are often lumped in with ‘system losses’. These include mainly feedwater heating (deaerator) steam use, soot blowing, burner atomizing steam (on oil), continuous blowdown, and bottom blowdown.
2) Condensate return volume may differ greatly between plants / systems and between individual customers on the same system. The greater the make-up, the greater the in-plant steam use (losses). Metering make-up water is the most common way to estimate this, provided plant ‘vented’ flows are deducted from total make–up. In systems in good condition, condensate losses in the distribution system returns should be minimal, so these losses should be attributed mainly to the end-users, rather than to the distribution system.
3) Differences in metering between steam sources (boilers) and the total of the individual customers’ meters are often attributed to ‘line losses”. David Christiansen of Univ. MN addresses this well in his reply.
4) A ‘constant load’ is a better way to account for line losses than is using a ‘percentage’ of total steam produced. For example, if the system operates for long periods at light load, the ‘line losses’ can easily be the largest load on the system, while if the system is moving a lot of steam constantly, the line losses will be a much lower fraction of the total. Under both of these flow conditions, the line losses are constant, but will result in much different ‘% system losses’ calculations.
Distribution system heat losses:
5) In a steady-state operating condition (when lines are fully warmed up), distribution losses are a ‘constant load’ which is determined mainly by these variables. While each can be estimated (‘wild-guessed’ is probably more accurate) and calculated, I wouldn’t trust these calculations alone. Instead, running these calcs can be a useful cross-check on the ‘accounting’ exercises listed above.
a. total length and diameter of the lines
b. steam temperature (distribution pressure)
c. amount and condition of the pipe insulation
d. depth of bury & soil conductivity
e. climate
f. condition of the drip leg steam traps (little blow-through)
Reports and “Hard Data”:
I have been able to find very little published and well-documented measurements on buried steam system losses. The information I have found comes mainly from some field investigations conducted in the 1990s by the US Army Cold Regions Research & Engineering Laboratory and it is difficult to say how representative these systems are..
One system in Nevada lost 58% of total steam generated each year in the distribution system. Total condensate return for this system was 46%, so by this measure, it was not in acceptable condition.
I hope this is of some help.
Best Regards,
Tom Phelps, PE, P.Eng.
Principal
Stantec
801 Jones Franklin Road Suite 300
Raleigh NC 27606-3394
Ph: (919) 865-7527
Fx: (919) 851-7024
Cell: (919) 522-3922
tom.p...@stantec.com
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Hugh Bahar
Here are some general answers to a general question:
Distribution line loss can be heat lost through piping and insulation or it can be the direct loss of steam through venting. If condensate is returned, there is some sensible heat lost through condensate subcooling on the way back to the plant, but it is usually minor. On a well maintained, direct buried or tunneled steam distribution system, the losses tend to be constant throughout the year. I believe our campus has about 25Klbs/hr loss in the steam distribution system.
Metering is the best way to understand distribution system line losses. Steam metering is difficult when winter and summer conditions demand a lot of turndown from the steam meters. Condensate can be metered more reliably and easily.
Understanding the customers and the distribution system are needed to calculate losses. If customer steam losses are large due to direct consumption such as autoclaves, humidification, blowing building traps, etc., or the distribution steam traps are blowing by or condensate is being dumped, they have to be understood and factored into the calculation or repaired so they aren’t a variable.
On an older steam distribution system with a mix of insulation ages and condition and a mix of direct buried and steam tunnel, you will meter:
Steam: Exported (boiler generated steam will not be the same as exported due to plant steam consumption)
Steam: Consumed by customer (it is often easier to measure condensate)
Depending upon distribution system design, other variables may need to be measured such as boiler makeup and condensate return flows.
An infrared flyover will help to highlight how well insulated the distribution system is, and where the losses may be concentrated.
Best,
Hugh
Hugh Bahar, PMP
Sr. Engineer
Cornell University, Facilities Engineering
201 Humphreys Service Building
Ithaca, NY 14853-3701
Email: hr...@cornell.edu
Desk: 607-255-3853
Cell: 607-592-2197
Fax: 607-255-8071
From: distribut...@googlegroups.com [mailto:distribut...@googlegroups.com]
On Behalf Of Len Phillips
Sent: Monday, August 26, 2013 5:39 PM
To: distribut...@googlegroups.com
Cc: jack....@we-energies.com
Subject: {Distribution Forum} Steam distribution system line loss
The following is posted on behalf of IDEA member Jack Powers of WE-Energies, Milwaukee, Wis., jack....@we-energies.com:
What percent of loss (line loss) should I expect to see in a large district heating distribution steam system of about 400 customers, mostly heating with some hot water, located in the Midwest?
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