Need help managing water temps on two different water loops

jdrudolp

Hello, I am trying to figure out how to balance my boiler system. I have a Lochinvar KHB155N boiler and a ZVC406 Taco 6 value controller. I have four zones, three that are old school cast iron radiators that I have set to 140F, and one that is connected to Runtal baseboard heaters in a basement I am remodeling that I have set to 180F.

The problem I'm having is that per the boiler operation manual (100305277_20000558126 Rev D Page 64), when two loops on different set points call for water at the same time, it will set the water temp to the higher temp. Unfortunately when my old cast iron radiators heat up to 180F they are HOT, and tend to overshoot the desired room temps for the upstairs, and then stay hot for hours. Some are also close to beds and I worry about the kids touching them accidentally, etc.

What I'd like to do is have the opposite happen, when both call for water I'd like the boiler to push the lower 140F water until such time that the cast iron radiator thermostats are at temp, and then go back to 180F if the basement thermostat is still not at temp.

Anybody know if this is possible, and if so, how to make this happen?

Thanks,
Jeff

ethicalpaul

The bed will be OK and the kids will only touch it once. Steam systems are even hotter and have been used for over 100 years.

pecmsg

the "Old School" cast iron radiators were designed for 180°F supply water. Kids only touch them once and learn, non-issue.

If you insist, Get a TACO ooE circulator installed and set it for a lower return temperature on the cast iron.

hot_rod

Do the rads need to run 180? Maybe 150- 160 would cover the load and lessen the over-shoot.

jdrudolp

The runtals can run at lower temps, they just don't put out as many BTUs. They have a table in their brochure with multipliers for lower temps. For example at 140 you multiple the BTUH output by 0.57, so essentially only half as hot. I have tried them warmer (like you suggest, I think 150/160) and it definitely helps the overshoot.

Any more info on the TACO ooE circulator? I will google it but if you have any info you can point me to that would be great!

Thanks.

pecmsg

https://www.supplyhouse.com/Taco-VT2218-HY2-FC1A00-Viridian-Delta-T-Variable-Speed-ECM-High-Efficiency-Circulator-Less-Flanges-Standard-120V?utm_source=bingad&utm_medium=sku&msclkid=83628f89ec5e1f3d3c90ee5accf91e6d

pecmsg

Unfortunately, with that boiler you don't want to operate above 140°F return water. You lose all the efficiency.

EBEBRATT-Ed

@jdrudolp

Just put a mixing valve on the loop you want to run at the lower temperature

hot_rod

Here is a de-rate chart for cast rads. I saw an app for this somewhere also.

https://www.expressradiant.ca/pdfs/product_classic_sizing_how_to.pdf

In many areas you are at design condition less than 2 weeks a years, so determine the room by room load, derate the rads for that load and see where you come out with SWT. I've run cast rads down to 120F and they still feel warm and put out some heat to the space.

Really no rule about running any heat emitter at a specific SWT or delta T.

It depends.