I have unwanted temperature increase that is occuring
due to 1) water friction and 2) cabinet temperature.
I am trying to figure out how much of the temperature
increase is due to each one,and what can be done about it.

I have a one month old 2008 Dynasty Oceana.
This is a 275 gallon tub, with two 7 bhp pumps.
With the heater off and both pumps on high,
(the heater is forced off when both pumps are
on high, confirmed with a meter) the water
temperature is going up 3 degrees every 20
minutes. Air Temperature outside is 70 or so.

This is a well-insulated tub(lots of foam on
the tub), and insulated cabinet (foil insulation
on all cabinet panels), and those big 7 hp motors
generate a lot of heat.

pump1 runs a lot hotter than pump2, I assume
because pump1 intake is through the two large
filters.

If I run the tub with the side panels adjacent
to the motors removed, the temperature increase
is less, a little over 1 degree per 20 minute
cycle.

If I run only pump1 on high (pump2 off), temperature
increase is smaller yet. Factory claims this is
expected, because pump2 water velocity is higher,
and they claim temp increase is due mostly to
water friction....My experiements suggest that cabinet
air temperature is also a factor. My guess is that
the parts of the water piping that are not insulated
are picking up heat from the hot air inside the
cabinet.

I am in discussions with the factory, and I think adding
a small 12V fan to vent the cabinet, with appropriate controls,
would probably help.

Any experience with a similiar problem, and suggestions for
solutions appreciated.

Believe it or not, this is an entirely normal situation - and I'm a bit surprised to find that a newer tub (these days) still has this happen.

Yes, absolutely - that tub can get to full blown overheat condition considering the design and implementation of the large pumps in there.

All this is telling you is that it was over-designed, and you are benefitting from excess heat generation from the pump motors... which is a good thing actually in the long term.

IMO your best alternative is to actually CUT HOLES in the equipment compartment, staple some screen mesh over those holes and allow the excess heat to ventilate.

Crappy situation with a new spa, but it's definitely a desired outcome when winter arrives and it's really cold outside.

BTW, this is everything to do with heat generated by the pump motors, and less than 5% - my personal best guess - due to actual friction. I could fight the factory estimates and people one one one but it would be a useless fight on theoretical grounds - I work in the field and see this stuff, most factory people do not.

(Not meaning to bash techs - but the line about water friction and it's 'in line' and you're getting 3 degrees in 20 minutes? I'm wondering what on earth they got in line with the pump plumbing to create such intense friction effect? Sounds more like they got a cabinet that's sealed too well to me - and the spa is soaking up all the pump motor heat which is MONSTROUS when contained!)

Just like yourself, you're making assumptions based on your own best judgement - because the spa is at your house, in your environment, and not sitting at the factory.

FWIW, this problem usually exists with spas that do NOT have the pump/equipment compartment isolated from the rest of the under-portions of the hot tub. If you had a thermal barrier between the pumps/equipment compartment and the rest of the spa, I might buy the friction argument - but even that is quite a reach considering how much it takes - and it actually needs to be an intentionally induced friction effect to get the results you're seeing.

Thanks for the feedback, it's good to hear from someone else who has had some experience with this.

I am working with my local dealer to help me put pressure on the factory, and they are agreeing to work with me to try out a fan solution for the cabinet, with some intelligent controls that I have suggested....I think the person I am dealing with at Dynasty is trying to blame too much of the problem on friction, to try and make me go away, but I have the local dealer firmly on my side, and that is helping.

The motors do not have a compartment that is thermally isolated from the tub. There is substantial insulation on the bottom of the tub, but of course there are portions of the water pipes that are not insulated and are going to pick up heat from the cabinet.

I think the spa has been optimized for cold weather, and while the components seem to be very good quality, clearly the warm weather thermal run away problem was not dealt with......As you say, the part of the design that captures the heat from the large motors is a good thing in cold weather, and I'm hoping that adding a properly controlled fan will minimize the warm weather problem. If the cabinet temp can be properly controlled in warm weather, then that really would be the most thermally efficient overall solution. I really like everything else about the spa, so I'm hoping that Dynasty will work with me and get this one problem fixed.