Mike Schreiner, engineering and operations director for Caleffi Hydronic Solutions, will lead an online webinar, “Zone Relay Controls for Hydronic Heating,” from noon to 1 p.m. CT on Thursday, Feb. 18.
There is no cost for the complimentary education series, Coffee with Caleffi, but registration is required.
Topics include:
- How to prevent zone pumps from running when a boiler is in warm weather shutdown
- The best way to control variable speed pumps
- The need for different water temperatures
- Valve and pump control communication
- Controlling multiple secondary pumps and zone valves
- How controls communicate
The following is a question-and-answer session from last month’s webinar, “Multiple Temperature Regulation in Hydronic Systems,” led by Jody Samuell, manager of engineering education for Caleffi.
Q: Can you quantify efficiency gains that might be obtained by supplying water to heat emitters at temps lower than what a boiler is producing?
A: The easiest way to quantify it is a boiler manufacturer’s efficiency table. These tables are based on return water temperature. If you look at the table for the boilers you use, as an example, you can see the efficiency at 120 Fahrenheit vs. 140 Fahrenheit.
Q: Does it matter which side the injection pump is on going to the heat source?
A: If you look at idronics 7, it does show the mixing pump on either side. The important thing is to ensure the balancing valve is installed in the other injection riser. Refer to idronics at http://www.caleffi.com/usa/en-us/technical-magazine.
Q: I use a mixing station with outdoor reset and mod/con boiler with separate outdoor reset for multiple zone staple-up radiant and second-floor panel radiators.
A: That is one way to go about it. Depending on the water temperature for the staple-up (hopefully with plates), another option may be to size the panel radiators for the same temperature. The panel radiator cost will increase, but the equipment cost to deliver the second outdoor reset will be eliminated. Additionally, the overall efficiency will increase since I am not mixing in a warmer water temperature in the return to the boiler.
Q: Viessmann boiler runs continuously as opposed to other boilers that ignite after a “TT” demand. Do you care? Does it affect efficiency or operation? Do you prefer one boiler strategy over another?
A: When I think of outdoor reset, my goal is to run with the lowest water temperature needed to properly heat the building. If I achieve this, I will be heating the building 60 minutes of every hour since this is how the building is losing heat. From an operating standpoint, the Viessmann boiler doesn’t run continuously, the pump does and the boiler fires as needed to maintain temperature. When I look at the two strategies, the results should be the same: constant circulation. If TT is holding the boiler pump off, it indicates no zones are calling , which means the heating curve is probably set too high.
Q: Will a system sensor from my boiler on the GS system outlet (load) side of the hydraulic separator help me track boiler modulation?
A: It is more about water temperature. It will ensure that regardless of the mixing that is occurring in the hydraulic separator, the correct water temperature will be delivered to the heat emitters.
Comment: You may want to add that it is always good practice to design around the lowest water temps.
Q: Yes, it does. If you have a non-condensing boiler with baseboard convectors, does it still make sense to run lower temps to the baseboard if, for example, outdoor temps are warmer?
A: Yes, there is something called the 3-to-1 rule that states if I lower my water temperatures by 3 degrees F, the efficiency will increase by 1 percent. Check out Richard Trethewey’s 12 Commandments of Comfort on the Web. Two things to consider: I cannot ignore the dew point, so there will be a minimum temperature I can drop down to and also the baseboard has a minimum temperature associated with it, so I cannot reset below these temperatures.
Q: I’d like to install a condensing boiler that does DHW (priority or not), large garage slab floor (2,000 square feet) and snowmelt with a 300K load. Recommend two separate boilers?
A: From a sizing and control standpoint, two separate systems may be order. The considerations that drive me in that direction are first, the size of the two loads will be quite different. The hours per year for space heating is much greater than the hours where I need snow melting. If I size the boiler for the total load, I may have a situation where the minimum firing rate is the building load. I hate to have a boiler that never leaves low fire. Next, if I am dong snow melting with a single system, I will use a heat exchanger to separate the glycol system for snow melting from the heating system water. I will have to run a boiler hotter to supply a heat exchanger than if I direct-connect the snow melting to the boiler. Additionally, I will need a mixing device to maintain the slab water temperature when the snow melting is calling. So the piping system and the control strategy then become more complex.
