Efficient hot water heating system 1

[zekeman]

I know that there must be a hotwater heating system out there that measures the outside temp and inside setpoint and then controls the boiler cycling and duty cycle to maintain the room temperature, allowing the circ pump to work continuously.
Who makes one and what are the pros and cons? I know one of the pros-- continuous heating for comfort.
Any comments?

 

[RossABQ]

Zekeman, I no longer have a radiant heating system, but as far as I remember, it had outdoor temp reset in its control system. In the relatively temperate area I live in, you would quickly cook if only 180 deg water were produced.

 

[imok2]

BUY any major MFG duel input controller, Honeywell, Johnson,etc. They used to be called "Master and Sub master controls".

 

[zekeman]

quote"Zekeman, I no longer have a radiant heating system, but as far as I remember, it had outdoor temp reset in its control system. In the relatively temperate area I live in, you would quickly cook if only 180 deg water were produced."

Ross, if you control the duty cycle as a function of inside and outside temperature, you modulate the boiler temperature, so at moderate outside temps, you will get a moderate average boiler temp sufficient to carry the reduced load. You won't cook under this controller.

 

[walkes]

Tekmar makes boiler controls that will do what you need. I have used them on small commercial and residential designs.

http://www.tekmarcontrols.com/literature/a.html

Tekmar's controls have been rebranded by numerous companies for different control strategies. Their literature link above should give you enough options for your requirements.

AERCO has their own C-more control panel that will modulate their condensing boilers as needed and incorporate an outdoor air temperature reset on the boiler loop.

 

[zekeman]

Close to what I was looking for. Thanks for the post.

 

[fishonthebrain]

Another product similar to the Tekmar is manufactured by Fuel Economy Ltd. and branded as the Savastat LC. (load compensating boiler control)

Since the Savastat product was available long before the Tekmar unit, it appears to me that the Teckmar unit may have been reverse engineered from the Savastat product to skirt the patents held by Fuel Economy Ltd's design. The main difference that I can see relates to how the unit senses boiler heat demand.

The Tekmar unit has a sensor downstream of the boiler, and monitors temperature decay when the boiler is off, whereas the Savastat sensor is mounted on the boiler return feed, (for which the patents are held) and the unit monitors temperature decay at the return. With this configuration, the unit only interrupts the boiler firing when the stat calls for heat, and the unit determins efficiencies can be achieved. This design makes more sense to me because load conditions can be monitored at the return in real time, whereas the Tekmar unit is affected by the boiler volume itself, thus reaction time is delayed by factors of boiler volume and flowrate.

Having said this, I believe that the Tekmar unit may be a valid soution for small boilers, or if you run your pumps all the time, however I would recommend the Savastat unit for applications involving commercial size boilers, or where you don't want to run pumps full time. Running pumps only as needed also provides a significant amount of additional efficiencies, which I feel tilts my favor toward the Savastat product in most cases.

From a cost perspective, the Tekmar units are significantly less expensive, so you will need to calculate an ROI if either product is an option. Typically I have found that if the boiler uses more than $15k of fuel per year, the Savastat unit easily cost justifies with an ROI under 24 months. If consumption is under $15k, the Tekmar unit will more easily cost justify.

I have seen both units in use, and have found both products to be very reliable regarding low failure rates. Either product can be expected to give many years of service. I know of Savastat units which have been in service for over 10 years. The Tekmar units just haven't been around as long to form a product life comparison.