Delta t across the evaporator (txv sanden sd7h15)

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Delta t across the evaporator (txv sanden sd7h15)

Postby Rj1234 » Thu Jun 30, 2016 6:12 pm

This is on an excavator with an automotive txv sanden AC system.
my question is what would be an acceptable delta t for an evaporator
The other day the outside ambient one foot from condenser was 95F(shade)humidity 50-70%
And out put from vent was 47F(Max ac)which is really good!
I measured before the evaporator (return) was 67F and after the evap was 38F(loss of 9F though 10ft duct socks)29f of delta t across evap .blower and evaporator have been cleaned and the ducting is linear and without sharp restrictions.
Since automotive AC systems change more rapidly (rpm,etc)compared to residential AC
Is this a test that's worth doing ,what are other techs doing for performance testing txv systems
Thanks everyone!
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Re: Delta t across the evaporator (txv sanden sd7h15)

Postby Tom Greenleaf » Fri Jul 01, 2016 7:31 am

Enlighten me if you would please. What is a "delta t" and why would you measure it?

Your performance looks pretty good for a system in those conditions so why are you doing anything?

"Excavator?" : You mean some earth moving machine? IDK - if exposed to excessive dirt and dust you tend to that like you would for this machine in general. Otherwise if working properly with no adverse symptoms I'd just forget this as not broken and don't touch it,

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Re: Delta t across the evaporator (txv sanden sd7h15)

Postby cornbinder89 » Fri Jul 01, 2016 3:50 pm

Delta (anything) is just the change in, so he is measuring the change in temp across the evaporator (temp in compared to temp out).
Since the bottom line is: are you comfortable? I don't think most people measure it. IF the system isn't preforming up to expectations, measuring the temp change at the evaporator may help tell you what is possibl, and if the there is bleed heat getting into the ducts somewhere.
More likely to come into play when engineers are designing the system, more of a theoretical maximum, I've never bothered to measure it.
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Re: Delta t across the evaporator (txv sanden sd7h15)

Postby Tom Greenleaf » Fri Jul 01, 2016 5:17 pm

Thanks cornbinder: OP - I see your point that in "theory" perfect evaporation across an evaporator should be equal from point of evap to exit.

Looked again you saw 38F at the thing and up to 70% humidity! IDK - that's probable just dripping or pouring out condensate, fins of evap soaked and still gives good vent temps. I'd give that high marks for working pretty well.

Just comment now: Temp lost thru ductwork. I measure my own all the time - good system of a car. They vary but many I'll say lose about 5F thru ducts and heat of firewall. That compared to fresh air temp monitored up front of grill came to that conclusion such that if one didn't work the plain "vent" setting is hotter than the air outside so just open windows.

Other is your return air temp is pretty cold but totally matters where you are checking if that all the evap gets.

If thinking of making output temp colder I would mess with it now but on a less humid day. Plenty of places lots higher than that but rare for where I am for extended times so no time for my own conclusions on what to expect as it certain conditions don't last long enough,

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