Outdoor Reset

John T_2

I'm in the process of setting up the controls for a job we're working on. It consists of very limited output joist bay heating , a small amount of imbedded radiant and Myson column rads. The joist bay heating and the Myson rads have been designed around a 150 degree max water temp and the imbedded radiant 125 degrees. I say limited joist bay heating because the application limits it to not much more than floor warming with the Myson rads and the imbedded picking up the balance of the loads.

My first thought was to use outdoor reset on everything with the imbedded loops being proportionally mixed to reduce the temperature. The floor heating (joist bay and imbedded) would circulate constantly without thermostats. The Myson rads which are being installed in every room would be controlled by six zone thermostats and outdoor reset.

My question is whether I should control the Myson rads water temperature with a thermostatic mixing valve instead of reset which would allow higher outputs during mild weather. I thought this might be desirable for a "quick" warm up during those days when temperatures are up and down a lot.

Of course simplicity is always beneficial (not that reset is simplistic). Am I over-complicating things?

Anyone care to offer their thoughts?

John T.

Bill Clinton

reset

A lot depends on how the system is used. Around here (N. CA), people like to turn the heat off when they leave for the day. If they have a seldom used zoned area, they will turn the heat way down or off for that zone.

When they come in in the evening and turn the heat on, is that reset just gonna give them tepid water an take two weeks to warm the joint up?

If there is gonna be an inside sensor for the electronic brain to factor in, which zone is it gonna be in? What happens if they leave that zone off.

What happens when guests come in and they turn on that unused zone?

What's the minimum temperature your boiler can run at? If you maximum temperature for your system is 150 degrees and the minimum return the boiler likes to see is 140 degrees, there's not much to reset.

I seldom use reset because of considerations above.

Bill

John T_2

Have been using

the Erie bb3600 and was planning to on this job also. There isn't a function (or sensor) for indoor temperature sensing only contacts for heat demand which could be closed a variety of ways. This would only give a heating "call" and would not be variable.

The 3600 does however allow for boiler return temp sensing which would protect the boiler.

During mild weather the only water temp available would be that determined by the reset curve. That is why I am thinking the standing radiation should not be controlled by reset (for the same type of reasons you had mentioned).

Thanks for the reply Bill!

John Taylor