Replies

1. 
   Wet_Head | Apr 02, 2002 04:04pm | #1

   Not near enough details.  Is this a radiant floor or otherwise?  And the boilers should be set up different.  They should alternate the lead boiler which will make for a lot longer life for both of them. 

   Was it set up as a primary/secondary loop system? Sounds like a good place for some tekmar controls which can control the boiler and the do the outdoor reset.  If it is RFH you for sure need to use outdoor reset if you are in an area with lots of temp swings.

1. 
   EdJW | Apr 02, 2002 06:21pm | #2

   WetHead,

   I live in the Chicago area.  I have radiant ceiling on the first floor and baseboard in the basement(family room).  There is a mixing valve on the system to supply different water temp to both zones.  I do like the fact that there is a way of alternating boilers since the primary boiler runs 95% of the time.  Is this a worthwhile investment?  do you have any idea what this would cost to do?  Not sure what you mean by Primary secondary loop system.  I believe the way it's set up is that the whole house runs off the primary boiler, if the temp drops below 10 degrees F then the second will turn on to keep up with the load.  -Ed

1. 
   TLRice | Apr 10, 2002 04:04pm | #3

   Primary/secondary is a term that refers to one of two ways to install and control water-based heating/cooling systems. The primary loop consists of a pump, temperature control (like a 3-way valve and bypass), plus some other water specialties, depending on the specifics of the system (such as an air separator, expansion tank, suction diffuser/chem feed. The water in this loop is at a contolled temperature and maintains a constant flow through the boiler and/or chiller (if applicable). As outside air temps rise, the boiler water (out) temperature is decreased. That is your outdoor air temp setback. Some controls are stepwise some are proportional.

   All the heating (and cooling) loads are connected to the system via secondary loops. These loads are typically controlled with 2-way valves that throttle flow through the device (coil, floor tubes, radiators, etc.,) to maintain a local thermostat setpoint.

   In a primary only system, either all the devices have 3-way valves to control flow to meet load (and local t-stat setpoints) or they "run wild" and load is controlled by the boiler modulating to maintain its preset outlet temperature. The former is prefered but more expensive to install. A variation of this is to have a thermostatic control valve (3-way) that recircs some of the return into the supply to maintain a set supply temp.