[budman21901]

This is my first experience with a pool dome. We have a new customer with a Commercial Pool dome. It's over 30yrs old, and many of the mechanical pressure relief dampers no longer work. It's sort of a mess. Anyway customer says main unit never had any issues maintaining 1.25" until this year. Now the backup is constantly kicking in, and it must be the motor is what they insist. The motor is fine. It pulls 17.5A with 203V at the static pictured. It's 3yrs old, but not by us. The wheels maybe dropping a few a CFM due to age, but if you can't maintain static It's going somewhere! They have all pressure relief dampers closed. I honestly think they have leaks in the dome they refuse to address.

I know how it is with fans and blowers. My question is about affinity laws for static pressure with this motor. I noticed that if you open a door of the dome Static pressure goes down, the amps go up. Is that equivalent to no work? Shouldn't it work harder too bring the dome back up? What I am asking is could a leak in the dome cause higher amps, and if the dome was tight and sealed, and pressure reliefs working as they should amps would stay down due to correct design load on motor.

I have also never thought of 100% outside air with those laws. I have always thought of them as having a return ducted in.

Motor pulley is 7"
Shaft Pully 14"
Distance apart is 36.5"

None of that has been changed from what I know of, and only thing I know that has been changed are motors, and 4yrs ago they got a new dome. Customer states they have no design specs, so who knows. I just want to better understand the affinity laws of this type setup, so I can confirm my Job is correct. We don't do the dome at all!

Any help is much appreciated! Thanks guys!

 

[WAYNE3298]

The fan laws apply no matter the application. It takes more energy to move air than to develop static pressure. If you open the doors and let the static pressure go down the fan current draw will increase without the fan speed changing. You do need to determine if you have dome leaks that are causing the problem or if the fan has a problem.
I would try a smoke bomb.

 

[71CHOPS]

Fascinating...I’ve never even heard of such a thing!! What a great idea!

If I were tossed into that situation, the first thing I would do is walk the outside structure, and check every single joint that touches the ground and any penetrations (doors, etc.). Find any leaks, use toilet paper, soap bubbles, etc. to find all the leaks I could.

I assume the Dwyer is a controller that is supposed to control the relief dampers based on pressure? Is it pneumatic? Electric? Or both?

Basically fan laws are fan laws. Doesn’t matter if it’s outside air or not. Regardless, you need to stop any hemorrhages before you can address the mechanical side. I used to deal with pressurized electrical and chemical safe rooms. If those rooms weren’t 100% sealed, there was no way you could maintain the space pressure.

 

[budman21901]

Thank you for the explanation. I kinda figured that, but wanted confirmation to be sure since I was in a unfamiliar application I have never seen before.

 

[budman21901]

It's all electrical that has been manually shut due to inability to hold pressure. That is exactly how I was thinking of it. If it's 100% sealed the reliefs would be a must to relieve pressure. The dome has leaks, and I just wanted confirmation on the fan laws to adress the issue. He insist on a new motor which we are installing for him, but we have told him multiple times that is not the issue.

I like the smoke bomb idea. I may suggest that to customer.

 

[Spitz]

How does that work in winter? Wouldn't it be raining in there? How is the air heated?

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[Spitz]

Could you run the fans with a VFD. Or are the relief dampers engineered as part of purging/exhausting the chlorine pool air?

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[mwitt]

I think an important distinction isn’t made here by other responses.

Are fan laws applicable? Of course they are, if you want to answer questions about how the system will respond the changing fan speed.

But then everyone starts mentioning closing up leaks. Fan laws won’t answer those questions however.

Here’s what I mean:

Fan laws will tell you that, if you change nothing about the dome, and assuming you make 1.1” static now and want to make 1.25” then you need to increase wheel speed by a factor of (1.25/1.1)^1/2 and the motor BHP will rise by (1.25/1.1)^(3/2).

However, if as other suggest, you want to know what happens if you seal up the dome, then you need the fan curve. Since your changing the system, fan laws really aren’t applicable anymore.

 

[71CHOPS]

In a positive pressure space, the amount of loss (or gain) due to leaks is a HUGE issue. The pressure differential is so small, any tiny hole can change everything.

 

[thatguy]

Have you completed the basic maintenance on the system yet? Checked for plugged filters, dirty blower wheel, worn pulleys and belt? Made sure there are no volume dampers that have decided to close themselves?

I’m not sure what components your system has, I’m not familiar with this type of equipment either but without knowing that the system is operating correctly then it’s too early to start troubleshoot for a problem.


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[buford]

Looks like you have some more amps you can use. I would verify clean blower wheels and worn pulleys and belts first , then up the blower speed using a VP type pulley and then fixed size if the pressure comes up.

 

[pecmsg]

*

Looks like you have some more amps you can use. I would verify clean blower wheels and worn pulleys and belts first , then up the blower speed using a VP type pulley and then fixed size if the pressure comes up.

 

[TechmanTerry]

What is the Mfrg Pressure Spec for the dome??? That photo of the dome does not seem to be "under deflated" due to not enough CFM/pressure.
Was that access panel open when you took your readings?
How are the press relief dampers controlled at the moment?

 

[TechmanTerry]

How about that Old Retired SeeBee-"NavyGuy" H-Talk Brother. Did you do anything like this dome during your deployments?????

 

[budman21901]

How does that work in winter? Wouldn't it be raining in there? How is the air heated?

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There is a heater on the Main fan to Heat the air entering the Dome. There is a secondary fan backup with no heat, and also a backup generator for power outages. You are correct it is pretty nasty feeling in there. I am sure if the dampers were in operation, and dome was sealed correctly we would have the correct amount of air changes needed to keep the air fresh, and it would feel much different.

 

[budman21901]

I think an important distinction isn’t made here by other responses.

Are fan laws applicable? Of course they are, if you want to answer questions about how the system will respond the changing fan speed.

But then everyone starts mentioning closing up leaks. Fan laws won’t answer those questions however.

Here’s what I mean:

Fan laws will tell you that, if you change nothing about the dome, and assuming you make 1.1” static now and want to make 1.25” then you need to increase wheel speed by a factor of (1.25/1.1)^1/2 and the motor BHP will rise by (1.25/1.1)^(3/2).

However, if as other suggest, you want to know what happens if you seal up the dome, then you need the fan curve. Since your changing the system, fan laws really aren’t applicable anymore.

Thank you for this info!

 

[budman21901]

We were going to do a larger pulley to grab another 100 cfm from the motor. Amps are all over the place. Sometimes upwards of 19.8 when they open a door for chlorine since dampers don't work. Worried we would be pushing it a little too much...

 

[budman21901]

What is the Mfrg Pressure Spec for the dome??? That photo of the dome does not seem to be "under deflated" due to not enough CFM/pressure.
Was that access panel open when you took your readings?
How are the press relief dampers controlled at the moment?

This is the first thing I asked for from the customer. It's all over 33yrs old, and nobody knows nothing! Kind of a shot in the dark with old equipment they won't replace.

 

[budman21901]

Update so far is i was there today. Searched the entire dome, and on the roof where it attaches to the blower area has a huge gap of leaks. There is also leaks at both edges of relief dampers. The blower area has a old relief that we tried sealing, but leaks back into blower area which just allows the blower to recirculate the same air into the Dome. The blower is not ducted to the outside, but merely uses fresh air dampers that are manually open.

I told you guys it was a mess! Any way he's calling in the dome guy to seal leaks, and we are giving him a new motor on his dime, because he wants it. I don't believe motor is the issue at all, but everyone will be happy at the end.

 

[71CHOPS]

Is this a public pool? If so, I wonder how the health inspector would feel about this space....