Taco SR501-OR

Hilly

Is there anyway to adjust your DDT on this is accommodate lower water temperature system?
My case. I want to have system design temperature of approx 135*-140* at 7* but I still want my domestic priority to run at 180* So from what I can tell on this board you set your outdoor design temperature for 180* output. Is there a graph available to determine what my 180F output DDT would be? So I assume I have to figure some algebra for 135@7* = 180@x*

Then I set my design on the taco for for whatever I can equate 'x' to.

archibald tuttle

Hilly,

I haven't seen the new 501-OR. I'm familiar with its forerunner, the 501-exp style that used an independent PC-700 or 702 controller for the outdoor reset.

But a 501exp would not have offered hotwater priority either because it is only one zone.

For that application the norm would be like a 503 exp or i guess 503-OR now.

and the third zone can be set for priority and you put your hotwater call to that.

If you are using the same pump and multiple zone valves the taco approach would be a ZVC control of some multiple greater than one instead. i actually bought one of those last week but i haven't opened it up and never used one before. i think it has priority as well.

don't know what kind of boiler you've got so some workaround may be possible but it still might be easier to get a multi-=zone relay and save the 501 for something in the future. (I keep a 501 around because occasionally i need a set of NC contacts and at least the older versions of the multizone relays did not carry that.

brian

Tinman

When there is a DHW demand on the control, the reset curve will be ignored.

Tinman

Sorry. I can see now that my response didn't answer your question.

Hilly

It's okay, I do appreciate the time your took though. It may give insight to the product for the next person though.

SWEI

The SR501-OR-4 is a one zone switching relay with ODR control. All you have to do to increase the boiler setpoint during temperature DHW priority is close a contact wired in parallel with the X X terminals. There is a wiring diagram the front page of the IOM that shows another way to do this (interconnect it with a zone switching relay that has DHW priority.)

Hilly

I have all the wiring under control, I do believe. I'll do up a schematic over the weekend if anyone feels that it would be more beneficial to them for understanding what I want. The only issue I have is that I want the boiler aqaustat set at 180* for the DHW override. When there's a call for heat the supply sensor will stop it's call based on the outdoor reset. The reset is designed to be set for 180* DDT supply temperatures. I want to have 140*water supply at 7 outside temp. Not 180*@7*. So I'm hoping I could simple find a figure to compensate... ie 180*@-5* would then have my reset curve hitting 140*@7*.
Maybe I'm over simplifying it in my head, but I figured there must be a curve or formula whereby I could achieve the outcome I'm looking for.

SWEI

Reset ratios can be a bit confusing. I haven't run numbers specifically for the SR501-OR-4, but here is an example from the iSeries-R valve:

Re-working the formula from the instructions, I get:

Reset Ratio X (72F - Design Outdoor Temp) + 72F = Design Supply Water Temp

so with a 10F Outdoor Design Temp, I get:

RR DSWT
0.2 84.4
0.4 96.8
0.6 109.2
0.8 121.6
1.0 134.0
1.2 146.4
1.4 158.8
1.6 171.2
1.8 183.6
2.0 196.0
2.2 208.4

archibald tuttle

maybe i'm missing something here, but there are no DHW contacts. SWEIs scheme is just a parallel demand call to the boiler or boiler control. there would be no temperature regulation effected at all by the SR501 in the case of DHW call.

BTW, i found this surprising when i realized the SR-503 exp exerts no temperature control when the priority circuit calls. Silly me, i assumed the supply temperature being read by the expansion device (a PC 700 or PC 702 typically) would be regulated to 180 and maybe that that would be a settable parameter.

Instead you get just the result that SWEI is suggesting and the boiler must be controlled by an separate aquastat for upper limit. a lot of modern boilers have upper limit logic but they often have built in ODR so if it is an older one you have to make sure that the boiler has some kind of limit on it separately.

it sounds to me like you are trying to set your design temp for water temp of 180 but none of these workarounds engage you design temp for DHW. There are no connections on the SR501 to alert it of DHW demand.

brian

Eric_32

deleted.....

Hilly

The boiler does have an High Limit Aqaustat that will be set at 180F.
The SR501-OR has a DHW dry contact that will override the outdoor reset and then the end switch will tell my aqaustat to fire the boiler, which will take it to 180*

archibald tuttle

hilly,

i see those contacts now. they have really made this purposive. the old SR501 used to be much more generic.

i haven't had time to read to see if the DHW terminals will trigger the circulator or not or if that is settable or if you're expected to stack a relay that pulls a separate circulator for DHW.

on the rest you're looking for 140 at 7 degrees if i remember right.

so the brochure shows the curves starting equal at 70 ( i think someone on here said 72 but the brochure shows 70 - not a big diff anyway.)

so you are going down 70-7= 63 deg. to outdoor design temp and you want to go up 140-70= 70 deg. to reach system design temp. that is pretty close to a reset ratio of 1 but if you do the math it is 63/70 = .9 deg system so for each .9 degree drop in outdoor temp. you want to reset a single degree. The control has you setting at 180 so the difference between 180 and 70 is 110 degress of system temp mulitply by the .9 outdoor drop is 99 degs lower than the base of the curve is where 180 should be or -29 degs. i think you are right at the limit of the control because it only goes to -30 (in the picture) but that should do it.

corrections from any algebra scholars gladly accepted but i think that is how you figure what to set the reset for.

brian