800,000 Btu's to heat a 2500 gallon spa?

Barry Engleman

> system in that application, could be sized for <BR>
> 200 BTU/ sq. ft. It should be sized to keep the <BR>
> area clear and dry, regardless of what those <BR>
> Colorado skies could dump on 'er. That's another <BR>
> 200,000 off the 800K. <BR>
> <BR>
> Maybe the PE has slip <BR>
> and fall lawsuit paranoia too :)<BR>
> <BR>
> hot <BR>
> rod<BR>
> <BR>
> _A <BR>
> HREF="http://www.heatinghelp.com/getListed.cfm?id= <BR>
> 144&Step=30"_To Learn More About This <BR>
> Professional, Click Here to Visit Their Ad in <BR>
> "Find A Professional"_/A_ <BR>
<BR>

Barry Engleman

800,000 Btu's to heat a 110 sqft surface area spa


I have an engineered specification for a heat exchanger which is heating a commercial spa that holds approximately 2500 gallons and has a surface area of 110 square feet. The spa is outdoors and it is used in the winter presumably down to as low as 0 degrees F outdoor air temperature. The spec is as follows: 800 MBH heat exchanger. Hot Side: 50% propylene glycol, 160 degrees F. entering, 135 degrees F. leaving, 70 gpm. Cold side: 100% water, 100 degrees F entering, 115 degrees F. leaving, 107 gpm. There isn't a bypass shown on the spa side so all 107 gpm goes through the cold side of the heat exchanger. The boiler heating it is a fan assisted non-condensing low mass boiler with 1500 MBH input. The boiler has four stages. The first stage is 500 MBH. The boiler and heat exchanger are piped primary/secondary (kinda!). There is a primary pump and a primary loop but the secondary circuit tees are not closely spaced. The secondary piping does have a 3-way valve shown in the mixing position. There isn't any spec or sequence of operation for the 3-way valve.

I would like some feedback on how well others think this system is going to work. I would also like to know what problems might be expected if this system if installed as specified. Hopefully, I have included enough information.

Thanks
Barry

hr

Too bad

you couldn't use a large condensing boiler like the PK or Gasmaster to drive the thing. Nicer yet, find one that you could run the spa water directly to! I've heard Munchkins have been directly connected to pool applications. Stage a few of those for a real high efficiency system

Here is an idea if you have to do it with that equipment. This was a drawing from Siggy's seminar I attended a few days ago. It shows how to use a VS pump, in setpoint mode, to feed the HX "A" side and protect the boiler from condensation. Seems like a much more reliable and easier to pipe method. It assures the boiler gets adequate flow, return protection, and full output to the HX. Run the pipe sizing through the HDS.

hot rod

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rb_6

Yikes...

Hi Barry how are ya?

That seems like a really outrageous load...even under those conditions...what heat up time are they asking for? I'm guessing this is a commercial application - ski hill perhaps...even still its a big load.

Robert Bean

hr

The 50%

glycol mix is going to hit you hard on pump spec. Is it a must? Could the boiler piping be insulated underground, or maybe electric heat cable traced for emergency freeze protection?

hot rod

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Barry Engleman

Now the specified pump size!

> you couldn't use a large condensing boiler like

> the PK or Gasmaster to drive the thing. Nicer

> yet, find one that you could run the spa water

> directly to! I've heard Munchkins have been

> directly connected to pool applications. Stage a

> few of those for a real high efficiency system

>

>

> Here is an idea if you have to do it with

> that equipment. This was a drawing from Siggy's

> seminar I attended a few days ago. It shows how

> to use a VS pump, in setpoint mode, to feed the

> HX "A" side and protect the boiler from

> condensation. Seems like a much more reliable

> and easier to pipe method. It assures the boiler

> gets adequate flow, return protection, and full

> output to the HX. Run the pipe sizing through

> the HDS.

>

> hot rod

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 144&Step=30"_To Learn More About This

> Professional, Click Here to Visit Their Ad in

> "Find A Professional"_/A_

Barry Engleman

I forgot the specified pump!

The specified pump is a B&G 60 1-1/2x1-1/2x5-1/4 70 gpm @ 10' of head. I wanted to suggest using a VS pump but not this one.

I agree the oversized heat exchanger is a marriage made in heaven using a condensing boiler. Condensing is what I am afraid it is going to do to the specified non-condensing boiler. Most of the time the spa will be satisfied before the boiler reaches a non-condensing temperature.

The engineer is insisting on all of this equipment.

Barry

Barry Engleman

I think its outrageous

Hi Robert, I'm good, how you been?

Outrageous, I agree. I calculate a 140,000 btu/h load to maintain the 104 degree F. spa temperature at 0 degrees F. outdoor air temperature. The July/August design load is more like 72,000 btu/h.

I haven't found out the heat up time they have to deal with but i assume they have all night after it is drained and cleaned. This is how it is usually done in ski hill country. They also have a 20x40 swimming pool next to it that wouldn't miss a few thousand gallons of 85 degree water to fill the spa with.

Thanks
Barry

hr

Spas in resorts

like that see tremendous loads. Dozens of people in small time frames. Folks that roll in the snow and jump in the tub, etc. Kids that plunk snowmen into the tub

I've work on and maintained numerous large tubs in ski areas. I fully understand why the engineer would oversize beyond even the typical PE fudge factor.

Customers never complain when the tub is always the correct temperature and able to maintain. Let the temperature fall even 3 degrees and the phone starts rining like it's the end of the world.

I'd stick with the PE spec, perhaps suggest a better piping and protection method. But I wouldn't mess with his calc. Better his phone ring than yours if HE misses the load. Although it doesn't look like he has. Don't let the owners have you value engineer the loads down

As well as low return temperature protection, protect that boiler against high temperature and no flow. As you know a flow switch, properly adjusted, and a high limit switch are a must. Cooked glycol really fouls up tube HXers. Then you will have a moaning, underperforming problem to deal with

Good to hear from you again.

hot rod

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Barry Engleman

Sorry hot rod, I also forgot the mention the snowmelt

There is also about a 1000 sqft of snowmelt for the area around the spa. It is designed to be heated directly from the boiler - no heat exchanger. The snowmelt secondary circuit also has a 3-way valve in the mixing position. No spec on this mixing valve either. That is the reason for the 50% glycol. The spa and the snowmelt are right next to the boiler room. The spa equipment is in the same boiler room. At least the boiler is sealed combustion.

The pumps specified should handle the 50% glycol. We have Trackhoes specified to do the work that Bobcats could easily do.

Thanks
Barry

hr

A snowmelt

system in that application, could be sized for 200 BTU/ sq. ft. It should be sized to keep the area clear and dry, regardless of what those Colorado skies could dump on 'er. That's another 200,000 off the 800K.

Maybe the PE has slip and fall lawsuit paranoia too

hot rod

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