An Olympic caliber relay, Part 2

 

BY PAUL ROHRS

contributing writer

 

Last month we talked about relays: what they are, how they work, how best to utilize them. This month I would like to build on that by looking at how industry professionals from coast to coast are using relays in practical and creative applications.

Rocky Pavey is the owner/operator of Rocky’s Heating Service in Fairbanks, Alaska. Rocky uses relays with his Energy Kinetics System 2000 boiler installs. Rocky stated, “The EK boiler has a ‘digital manager’ that provides power to the thermostats. It also provides power to the zone valves. Closing the zone valve kills power to the zone contacts, relying on a ‘spring return’ style zone valve to pull itself closed. If we come across a system using White Rogers 1311 or 1361 zone valves where they are ‘power open/power close,’ then we have to leave their 24-volt transformers connected. This presents possible conflict between the System 2000 digital manager’s transformer and the zone valves transformer.

 

“We use the RIB brand, single-pole single-throw (spst) relay to connect to the tail switch contacts of White Rogers 1311 and 1361 series zone valves. Then the output side of the RIB becomes my thermostatic demand to the digital manager, preventing any butting heads of transformer power. It keeps us from having to replace some perfectly good zone valves when using the System 2000 boiler controls.”

 

Brad White is a highly respected engineer from Boston. White said, “I am partial to Veris Hawkeye current sensing relays. They are roughly sixty bucks and can be panel mounted or in a junction box. Some uses I have in play include: interlocking combustion air fans with a clothes dryer; make-up air fan with a cooking range hood fan; lock-out or enabling of pumps and/or fan coils (not running a fan until water flow is established) to prevent freeze-stat lockout. This allows the return temperature sensor to be satisfied in series, too. These are just a few of its many applications. Also the #735 can detect amperage spikes indicating a fan belt break or sheared pump coupling.”

 

A lot of snowmelt systems use circulators with high amp draws. I use relays to isolate and protect circuits in the system when these circulators have the potential to trip breakers and blow fuses. Figure 1 illustrates a two-zone snowmelt system with one heat source. Figure 2 shows the electrical schematic of the controls and boilers that are controlling this system. We can refer to Figure 1 for piping and visual references and to Figure 2 for the bulk of our discussion about how relays 1 to 3 are used and what their functions are.'

FIGURE 1

 

FIGURE 2

The Tekmar 665’s featured slab sensors (S5 and S6), when coupled with the outdoor sensors (S3 and S2), will activate the system and start melting snow through terminals 11 and 12. When the snowmelting call for heat begins, 120V is switched through terminals 11 and 12. We use this circuit to power the coil on our relays on terminals 7 and 2 on relays R2 and R3. With the coil now closed, we can highlight two functions on each relay. First, upon energizing the coil, the NO (normally open) terminals 1 and 3 close and allow it to complete the circuit back to our boiler TT of our Lochinvar Knight boiler. This signals the call for heat, and the boiler initiates its firing sequence to inject heat into the system. Secondly, when the coil is energized, relays R2 and R3 allow terminals 8 and 6 to switch 120V(ac) power to complete our circuit to the P6 and P3 circulators.

 

Now let’s look at our Knight boilers control board. With the Knight boiler, anytime there is a call for heat via the room stat or end switch terminals, the system pump contacts are engaged. Even if the domestic hot water (dhw) circulator is used and the boiler pump drops off, the system pump contacts remain engaged until the call for heat ends. This feature is used to our advantage by driving the circulators that provide heat to the heat exchangers. The Knight boiler system pump contacts will allow up to a 1.8 amp draw (the larger Knight XL series has dry contacts that can switch up to 30 amps), but our P2 and P5 circulators are going to draw 3.0 amps each, so use the R1 relay to protect our system pump contacts.

As said earlier, the system pump contacts remain engaged constantly during a call for heat, so we are going to use those contacts to close the 120V(ac) coil of our R1 relay to switch a dedicated and appropriately sized circuit (Circuit #1) to our P2 and P5 circulators. When the system pump contacts engage, it powers the coil on terminals 7 and 2 and allows our NO contacts to close so that terminals 8 and 6 safely feed the necessary power and amperage to our circulators.

 

With the use of three dpdt relays on this job, we safely switched the necessary voltage and required amp draw to our P2 and P5 circulators, switched power to our P3 and P6 circulators and completed the low voltage circuit to signal a call for heat to the boiler. As with any heating or snowmelt system, proper programming and selection of controls is essential to proper operation. Hopefully, relays and their proper wiring will be second nature to you, and heating contractors across the country will be using these handy and inexpensive devices to enhance their heating systems.

 

Paul Rohrs welcomes your comments. Contact Paul at paul@biggerstaffradiantsolutions.com.