300 room 10 story hotel...no hot water during low demand?

[getyourbone]

• 300 rooms
• 10 story building
• 2 large boilers on roof with enough capacity during high demand - one is newer.
• no storage tanks
• recirculating system to provide "instant" hot water for each room
• Recirculating pipe is only 3/4 inch running length of roof with about 15 1/2 inch branches going down to the rooms.
• only 1 pump (on roof) on recirculating system for 300 rooms - pump recently replaced
• building built in ~ 1987

Guest. periodically report "no hot water" but it is not only upper floors or lower floors or furthest from boiler...???

it is never more than 1 - 2 guests per occurence that report an issue.

We have only been able to narrow it down to "low demand" periods such as 4 am or evening with low occupancy.

Any ideas what kind of issue we are encountering. air lock? Do we need a bleeder valve? if so, where should it be installed?

Should we create "zones" and install a circulating pump for each one?

other ideas

 

[Jadnashua]

The recirculating pump may not have enough head or there may be air trapped in some of the lines. Normally, this would be purged out, but if there is a leak, it might get added. 10-stories means a fairly big pressure differential, and putting in the wrong pump might just mean problems.

 

[Sponsor]

 

[hj]

Circulation systems do NOT lift water, they move it around so "pressure differential" is NOT a factor, but friction loss IS. A recirculation system with even TWO connections needs a method to balance the flows, one with 15 connections would be impossible to regulate without a lot of fine tuning, and even then it would probably need a "special" pump, not the "blue light specials" that would normally be used. The reason it works during high usage, is that they maintain enough flow to get the piping hot and keep it that way. When there is little use, the users would have to evacuate GALLONS of cool water and also heat up the piping so the water would stay hot until it got to the rooms, and they would probably NOT want to take the half hour or so to do this before getting a shower. The type of shower valves can also be a huge factor. IF they are Moen or Mixet they could also contribute to the problem.