Variable and weak water pressure at a small hotel

[Bassosa]

Hi guys,

I'm attempting to fix a water pressure issue at a 16-room hotel with two retail spaces on the ground floor. Don't plan to do the work myself but want to be knowledgable before I let the contractor form his thoughts on the problem.

Trouble is that the water pressure is weak but also surges when the pumps come on.

So on the ground floor we have two 2hp water pumps pressuring the system, with an added 80 liter (I believe) pressure tank. Two 5000 liter in ground water tanks.

(We don't have the option to store water aloft in say a day tank or something)

On the ground floor we have 
 

5 toilets & bum gun (both on same outlet)
8 faucets
1 garden hose
1 shower & 1 washing machine

The hotel rooms are on the first and second floor. Every room has 1 shower, 1 faucet, 1 toilet & bumgun (same outlet), so 3 outlets per room for a total of 48 outlets.

 

Curious to find out how you guys would create stable, adequate water pressure for satisfying showers?

My initial thought was put the full ground floor on a separate system by buying a 1000 liter above ground tank and a domestic water pump and let the existing system only deal with the hotel rooms on the first and second floor.

Thoughts? 
 

[OneMoreFarang]

Did it ever work?

Because if it worked at some time in the past then maybe it's only necessary to fix something which "went wrong".

If it never worked, then that is a different story.

 

One thing which (some) Thai plumbers seem to have difficulties to understand is that if you have somewhere a bottleneck in form of a small diameter pipe, then that will restrict the flow after that.

There should be "big" main pipes and then maybe smaller pipes to the rooms and outlets.

A couple of outlets together will never work properly if the (main) pipes are not big enough.

[Crossy]

Good point from @OneMoreFarang

 

Is the pressure OK when the pumps start?

 

I wonder if the pressure tank has lost its pressure / become waterlogged?

[Bassosa]

14 minutes ago, OneMoreFarang said:

Did it ever work?

Because if it worked at some time in the past then maybe it's only necessary to fix something which "went wrong".

If it never worked, then that is a different story.

 

One thing which (some) Thai plumbers seem to have difficulties to understand is that if you have somewhere a bottleneck in form of a small diameter pipe, then that will restrict the flow after that.

There should be "big" main pipes and then maybe smaller pipes to the rooms and outlets.

A couple of outlets together will never work properly if the (main) pipes are not big enough.

Spot on. 

He used same diameter pipe throughout whereas the main lines (the tree trunk so to say) should've been bigger. To change that we would need to get a sizeable drill inside the duct shafts to redrill bigger holes. Not sure if that's even feasable.

The system has never worked properly. It's a poor design. We've always had poor water pressure but it only manifests itself in the shower. 

The surging has been better (as in less bad), especially after a service, but soon after goes back to its old ways. Can't even run a sprinkler in the back garden to water the grass. It goes from a piddle to full on fountains at the Bellagio and then back to almost nothing.

[OneMoreFarang]

1 minute ago, Bassosa said:

Spot on. 

He used same diameter pipe throughout whereas the main lines (the tree trunk so to say) should've been bigger.

So just replace all those pipes, problem solved. ;)

 

 

[Bassosa]

53 minutes ago, Crossy said:

Good point from @OneMoreFarang

 

Is the pressure OK when the pumps start?

 

I wonder if the pressure tank has lost its pressure / become waterlogged?

Yes, when the pump(s) are firing the water pressure is good. As soon as they switch off (pressure setpoint reached) the pressure drops.

 

 

[Ben Zioner]

Two of those. Your guests will love them.

[degrub]

Variable speed motors driving the pumps simplifies the controls at the expense of higher initial cost. And stage the pump on demanded operation so both don’t  run unless needed. Multi pump controller should be able to use equivalent to pump curves to manage the combined operation and avoid sudden bumps in flow or pressure at the users. Need to figure out a design max flow case ( assumed number and type of users one at one time ) to avoid the superbowl commercials effect on pressure.

 

if that is a bladder pressure buffer tank, best to keep one in the system to ride out short demand spikes. As Crossy suggested, the existing one may be waterlogged. They require minimal, but routine , maintenance.

 

Also, if it makes sense, consider reworking the pump piping so that one pump can run independently in the event you have to work on the other. The system will be at reduced capacity, but for a hotel, having some supply could be beneficial.

[Bassosa]

56 minutes ago, degrub said:

Variable speed motors driving the pumps simplifies the controls at the expense of higher initial cost. And stage the pump on demanded operation so both don’t  run unless needed. Multi pump controller should be able to use equivalent to pump curves to manage the combined operation and avoid sudden bumps in flow or pressure at the users. Need to figure out a design max flow case ( assumed number and type of users one at one time ) to avoid the superbowl commercials effect on pressure.

 

if that is a bladder pressure buffer tank, best to keep one in the system to ride out short demand spikes. As Crossy suggested, the existing one may be waterlogged. They require minimal, but routine , maintenance.

 

Also, if it makes sense, consider reworking the pump piping so that one pump can run independently in the event you have to work on the other. The system will be at reduced capacity, but for a hotel, having some supply could be beneficial.

Thanks for your comments although I was hoping for a simpler solution than dishing out hundreds of thousands on new pumps, motors etc. 

The pressure (bladder) tank does emit air at the nozzle. It is pressurised at regular intervals by a contractor using a simple electric air pump. Does this rule out waterlogging?

[degrub]

Waterlogged -

https://waterdefense.org/water/well/waterlogged-pressure-tank/
 

Alternative to variable speed drive would be to use a recirculation flow back to the storage tanks controlled by a pressure regulator. Pump motor could be  two speed design to reduce electric consumption from recycle flow and pressure bump. Basically, a less expensive variable speed motor.  More expensive to operate. Need extra control logic to prevent pump from staying on and just recycling although should be able to handle by undersizing the recycle valve. 

The issue is the centrifugal pump head versus flow curve is usually flat near 0 flow, max head pressure, so the flow goes from 0 to 50+% design flow without much change in head pressure. High pressure switch may not trip the pump when recycle is flowing. 

[Bassosa]

Thanks. Confirmed that its NOT waterlogged.

[Bassosa]

Not giving up on this topic just yet. Surely there has to be away to improve things with what we've got?

Attached a pic of how the water travels up. A clear split into the left side of the building (8 rooms) and the right side (8 rooms).

Could we remove the split and run two pipes to the pumps, then assign one pump per side of the hotel? Perhaps add a pressure tank so we have a pump/pressure tank combo for each side of the building?

[Crossy]

19 hours ago, Bassosa said:

Thanks for your comments although I was hoping for a simpler solution than dishing out hundreds of thousands on new pumps, motors etc. 

The pressure (bladder) tank does emit air at the nozzle. It is pressurised at regular intervals by a contractor using a simple electric air pump. Does this rule out waterlogging?

 

Not necessarily.

 

Ideally, remove the tank and then pump it to the recommended pressure (should be indicated on the label), that should remove one of the variables.

 

The tank shouldn't need to be regularly pumped up, that it needs it is an indication there's something amiss.

[Fruit Trader]

3 hours ago, Crossy said:

Ideally, remove the tank and then pump it to the recommended pressure (should be indicated on the label), that should remove one of the variables.

 

The pressure tank label will likely show the tanks max operating pressure.

 

Bladder tanks are normally charged to approx 1-2 psi below pump cut in pressure with the water side fully discharged. 

[Bassosa]

Thanks for all your comments so far.

Our pump guy isn't helping much so I may need to have a go at it myself. Real lack of knowledge about these things in Chiang Mai. 

I first want to adjust the two pumps setpoints and the pressure tank, just to rule out the possibility the contractor got kg/cm2 muddled up with PSI. Just a suspicion that one but those things do happen. Our gauges only display kg/cm2

Right now, the pump come on at 1.5 kg/cm2 (~23 PSI - seems low?)
Shut off is at 3.5 kg/cm2 (~50 PSI - seems about right?)

No idea what value the pressure tank is set at. Will have to drain the system for that first. I do know that its functioning and not waterlogged.

I want to go to:

ON: 2 kg/m2 (~30 PSI)
OFF: 3.5 kg/m2 (~50 PSI)

Then pressure tank at 1.8 kg/m2 (~27 PSI). I bought a handheld compressor for the purpose.

Sound idea? What am I missing here guys?