Boiler Control System

[tmy23]

Greetings.
We have 2 Weil-McLain HE boilers and a domestic water tank. This was installed 9 years ago and to save $$ we went without the boiler control system. The system is set up with one boiler primary heat, the other priamry hot water and when it's below 15 degree outside, the second boiler boiler kicks in for heat also.

I now want to zone and want to install a boiler control system. Are their any recommendations regarding price vs. guality/features?

thanks...

[LazyPup]

This question is a bit confusing. For the most part boilers have a self contained control system to maintain temperature and pressure within very tight preset ranges and limits.

In turn, any control system above and beyond a basic thermostate to turn the system on and off would more properly be defined as a climate control or enviroment control system, which would control not only the boiler on and off functions, but would control the lead lag function of multiple boilers or control specific peripheral components in the heat distribution system, such as zone valves, circulating pumps, forced air blowers etc.

In order to express an opinion of your proposed control system we would need information on what it is designed to control

Given that you already have two boilers it should not be difficult to establish a two zone system, but would most likely require some major re-piping throughout the structure.

[tmy23]

Thanks for the reply. Not beinga professional I probably didn't state my question correctly. I was interested in installing a system that would (1) cycle the boilers (2) manage the demand for heat along with the demand for domestic hot water (3) manage the heat to the zones (now 2 zones, possibly more in the future).

I know that Weil-McLain has such systems, but (unless I don't understand their literature) to get to a system that will manage the domestic hot water tank, you have to step up to a controller that will handle 4 boilers. I really don't need that capacity and from a price/quality standpoint was wondering if anyone had experience with this type of equipment and had opinions on a manufacturer for a "controller" to manage the two boilers, hot water, and zones?

Does this help??

[LazyPup]

The type of system you currently have is common in commercial structures and occasionally used in larger residential homes. Once the worst case scenario BTU heat demand is computed for the structure, rather than install one boiler capable of meeting that demand, two boilers 1/2 the peak demand are installed. This type of system works very well in cold climate regions, where mid winter temps require both boilers to meet the demand, but during spring and fall one boiler working alone would meet the need. The advantage is reducing the fuel requirement to 1/2 during light demand while still retaining the ability to meet peak demand.

When a system is installed in this manner a Lead/Lag control is installed, which periodically switches which boiler is the primary and which is the secondary. When operated in this manner both boilers will have approximately equal operating time which extends the life of both boilers.

When multiple boilers are installed in this manner they both feed either steam or hot water to a common header line, which then goes to the distribution system. The distribution system can then be divided into zones by thermostatically cycling the individual zone circulation pumps, steam valves or air handler blowers. (I once operated a system in a school that had two boiler rooms, with 3 boilers in one room and 2 in the auxillary boiler room, all supplying live steam on a common header. The building was then sub-divided into 18 zones.) This type of system is very practical in a large structure such as a school or hospital because in this manner, any individual boiler can be taken offline at any time for maintenance without adversely effecting the overall heating system.

While it would certainly be feasible to install such a system in residential enviroment in most cases it is not practical. Keep in mind that the more complex a control system becomes, the more maintenance it will require, and often such a system is beyond the expertise of many residential heating contractors, which would obligate you to use the services of a more expensive commercial boiler service company.

The simpler solution for you to devide your present system into two zones would be to simply divide the distribution system into two parts and operate each zone from a separate boiler. Thus if the house were divided with the living quarters area on one zone, and the sleeping area on the other, you could then operate each boiler with a relatively inexpensive programable setback thermostat. In this manner, one boiler would be on peak demand while the other is on the setback, and it would change by day and nite, which would primarily maintain equal operating time on each boiler without resorting to elaborate and expensive control systems.

When domestic hot water is produced in a boiler, it is done by means of a separte closed loop within the boiler. You could then combine the closed loops to a single header and install aquastate sensors and zone valves on the individual boiler loops to insure it is calling hot water from the boiler that is firing, then install a conventional water heater to supply hot water during the non-heating season.

By setting the system up in this manner it would use common off the shelf control components which would minimize future maintenance costs.

[tmy23]

Thanks for the reply. I do appreciate your input on maintenance. When this was originally installed, heat came from boiler #1, hot water from boiler #2 and boiler #2 was standby for heat based on an external temperature sensor set at about 20 degrees. THe original contractor went out of business, since then sections have been "repiped", i.e. another contractor took the "header" out and installed the output from boiler 1 into the input of boiler 2, in effect hooking them up in series. I'm not sure that boiler 2 comes into play anymore except for hot water and thus I'm using a $1500 boiler to heat hot water and it might not provide heat anymore, I have to test that when it's cold outside. Presumably when he re-piped the system he changed the external temperature sensor settings, or disconnected. Unfortunately I learned a lot of this after the fact, meaning I've had to become semi-literate in heating to "decode" what these guys have been telling me.

I don't have balanced zones, I live in an old "barn of a victorian" in NJ where 95% of the house, living and sleeping quarters are on one zone. Many of the distribution runs are in series, running vertically from radiators on the first floor up to bedrooms above on the 2nd and 3rd floors so zoning looks problematic, maybe thermostatic radiator controls?

My kitchen and laundry room at the back of the house are COLD due to large windows and heat loss issues which I'm working on. The laundry room is on a separate zone, heating 3 small baseboards, installed since I bought the house. Each room (kitchen and laundry room also has an original cast iron radiator which are both still on the (95%) main loop. At the same time as putting in a multi boiler controller, I was thinking of connecting all this (baseboard and 2 cast iron radiators) into a single zone.

I've been concerned that I've paid for this supposed great system with two boilers and I'm not really getting the splitting of "load" across the two boilers and also probably not getting the best advantage of matching the boiler demand to external temperature differentials. I've been through 3 contractors who have good references and claim they know what to do, and I end up with "repiping" and other changes that sounded good coming from the "pro" at the moment, now in retrospect, seem like a mistake? I've tried Weil McLain, but they won't recommend a contractor, and won't send out and engineer unless requested by a contractor.

And finally, although all I ever wanted was to turn on the thermostat and have economical heat by necessity I'm learning a little about this stuff and was wondering if dumping another $1,000-$2,000 into having one of these controllers installed might ultimately be more economical from the standpoint of boiler life and energy usage?

[LazyPup]

Once both boilers were interconnected by the common header, for all intents and purposes the water vessels became one boiler with two burners.

While you certainly can install an outdoor temperature sensor, in practice it is not required.

fundamentally boilers have a self contained control system which simply maintains the vessel at a preset temperature or pressure range.

On a circulating water system the boiler control senses the temperature of the water returning from the loop. When the return loop temp drops to a set point the boiler turns on and runs until it reaches its preset cutout point.

In turn, the radiaton on the circulating loop changes constantly by the differential of temperature between the room air and the radiator. When the air is cold it absorbs energy at a faster rate than when the room is warm. The increased absorption of BTU energy into the room air, drops the temperature of the water on the return loop.

The second boiler is then set up with a control that senses the return loop temperature and the primary boiler run status. When the primary boiler is firing AND the loop return temp is below the preset low limit, the second burner fires to assist the primary burner. Although it can become a bit comples, each individual room or zone can be set up with individual thermostats that control zone valves on the loop. As a room is satisfied, that valve closes. (This is the manner that motel rooms are controlled when heated by a master boiler system.)

The individual room or zone thermostats should be wired in series through a strap on aquastat sensor that makes sure the supply line is hot before opening the valve. When configured in this manner the main control for the boiler can be either a master thermostat of a manual on/off switch.

[tmy23]

Lazypup,

thanks for your assistance on this. I'll repeat so that I understand.

(1) external temp sensing in unnecessary because heat loss in the rooms (which varies with external temperature) will determine the need to keep the system water hot.

(2) having individual zone valves connected to the thermostats will limit heating to the areas in demand.

(3) hooking the thermostats in series will insure that the system water temp (and circulator) are kept running as long at one of the zone thermostat aren't "satisfied".

This won't help me though with boiler wear and tear, I guess the question is where to find an engineer or expert who can advise on whether there's a payback to anything more than (i.e. boiler controller) the setup you've described?

[LazyPup]

You are correct on everytning except the thermostats...The thermostats are not interconnected. You require ONE thermostat or on/off switch as a master for the system which simply tells the system when you require heat and turns the boilers on. Once the boilers are turnen on they are controlled by the differential temperure on the loop return line.

When additional thermostats are installed to control zone valves, they should be put in series through a strap on aquastat sensor that senses the temperature of the supply line from the boiler. In that manner they will not unnecissarily activate the zone valve unless the supply line is hot enough to provide heat.