Another Snowmelt project

CBRob

Heated driveways are really catching on here in Crested Butte.

The last few I've done have had a dedicated modcon boiler.
I'm planning out another one that is going to share the home CH boiler.
It's oversized a little and will be able to keep up with both the home staple up under floor and the driveway.

The ones I have done so far used the mod input from the tekmar 654.
Because this boiler is getting a TT for CH1 I don't have the option of  modulating the boiler with the tekmar 654.
I'll have to go with an pulse width injection pump or mixing Valve I think.
For effeciancy and reliability, is one better than the other?

The boiler is an instinct solo 199.

Zman

There are plenty of ways to slice this one. You should keep in mind that the snowmelt system when starting cold, will drag down the boiler and possibly leave the house a bit cold.
I would recommend a control strategy that allows the control system to prioritize the heating and DHW over the snowmelt.
Tekmar has some nice solutions that will control the boiler using the 0-10 VDC connection and then manage the loads as you please.
How big is the house and the snowmelt system?
Are you planning to use a heat exchanger or glycol the whole system to 50%.
@Mike_Breault could get you pointed in the right direction.

CBRob

Zman, as always thanks for sharing your knowledge with me.
The house is 3000 sq feet.
The previous boiler was a triangle tube 150k modcon. The HX bolt popped off like a typical T Tube from 15 years ago.
I replaced it with a 199k

The house is well insulated and has an r60 attic.. the old boiler kept up fine with heat and the indirect water heater.

The boiler will give priority to DHW, but has only two setpoints for CH.
I can't use the modulating input at the boiler from a tekmar 694 if I'm using a TT signal from the thermostat relay for the house.

If it gets a signal from both Ch1 and Ch2 it will go to the hotter setpoint.
The tekmar snow control allows me to set intervals for the snow melt to turn off and let CH get full heat from the boiler.

I'll definitely use a dedicated loop of 50% glycol and a heat exchanger so that the whole house doesn't share the glycol from the snowmelt.

Tekmar has a boiler type setting of MOD that deliver the 0-10v or ENBL for pwm  output.

Tekmar suggests using those output for a variable speed pump or mixing Valve.

The house has both infloor and staple up radiant heat.

@Mike_Breault

Any advice for controlling a pump or mixing valve with the 694? Is it even needed?  Maybe just run the boiler on/off and use a heat exchanger?

CBRob

The burn mark from the snapped off bolt on the HX

Zman

A Tekmar TN4 boiler controller will tie it all together for you. Your present heat call will connect to the boiler controller rather than the boiler itself. That will free up the boiler to take the 0-10 signal.
Tekmar used to make a snowmelt controller that would limit delta t thus keeping the snowmelt from dragging down the boiler. That model was discontinued.
How big is the snowmelt area?

CBRob

The snowmelt area is about  900 SQ ft.

I'll start learning about the TN4

Thanks.

I've been learning a bunch from the coffee with calieffi videos.
They cover so many topics.

CBRob

There is one circ pump for all of the CH zones, very typical for installs around here.

I'm pretty sure that if I try to set up the boiler to respond to the mod 0 to 10v signal it will no longer respond to the TT signal 

CBRob

this is from tekmar, replace the second set of tees with a heat exchanger? The boiler loop would be a secondary loop. Use a alpha smart pump to inject using the 0 to 10v signal. This would be a setting of MIX

The other setting I think is an option is ENBL witch would fire the pump single speed and just adjust the on time interval based on slab temp.


I think that when on ENBL the 654 allows for an intermittent snow melt priority, so the house can get dedicated heat for a certain time.

Zman

The way you are planning to pipe it should work.
I think you will need more on the controls side.
My experience with the 654 is that it promises a bit more than it can do. It will run a 0-10 VDC mixing valve or circ. I do not think it can prioritize loads.

Mike_Breault

Good day, weird days chez tekmar, as we get a lot of calls, so apologies for the delay.
you can use a HE. we have the designs on that as well.. check out the 670 applications brochure.https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/81829-source/670-a-01 A670-3

the 670 will run a Modcon.

you "could" cheat the system on the boiler side using a pump control box like a 306P, and have the boiler enable come from that , connecting a SM control to the Priority zone.

SM has boiler priority, but will allow other zones to heat after 60 minutes

the 654 offers SM zone priority, not system priority (so if youhave more than one SM zone, you can prioitize them. but the heating system will not be a part of that.

thats when you need to get into a TN system, where we can do that. if you get into a TN system, I would advise you get ahold of your local rep as there are too many variable to go through here onthe Wall..

you can find your rep here https://www.watts.com/how-to-buy-sales-representative

be well!

CBRob

Mike_Breault said:

Good day, weird days chez tekmar, as we get a lot of calls, so apologies for the delay. you can use a HE. we have the designs on that as well.. check out the 670 applications brochure.https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/81829-source/670-a-01 A670-3 the 670 will run a Modcon. you "could" cheat the system on the boiler side using a pump control box like a 306P, and have the boiler enable come from that , connecting a SM control to the Priority zone. SM has boiler priority, but will allow other zones to heat after 60 minutes the 654 offers SM zone priority, not system priority (so if youhave more than one SM zone, you can prioitize them. but the heating system will not be a part of that. thats when you need to get into a TN system, where we can do that. if you get into a TN system, I would advise you get ahold of your local rep as there are too many variable to go through here onthe Wall.. you can find your rep here https://www.watts.com/how-to-buy-sales-representative be well!

Hello Mike. Thanks for the reply,.
I was thinking about using the 654 and use the pulse width modulation for control. It looks like that would work and be a fairly low cost option.


Is there anything to gain from using an oversized heat exchanger?

Zman

I think Mike is urging you to use your local rep for design help. Shamrock Sales in Denver has excellent reps dedicated to helping with Tekmar designs.
There is no harm in oversizing the heat exchanger as long as you don't go way oversized (and end up with laminar flow, which is hard to do). Most manufactures have calculators to help with sizing.

CBRob

Ill reach out to shamrock and my local rep.

The pulse width modulation is not the European way of controlling a pump, but just turns the SM pump on and off and allows the CH for the house to take turns.
As the slab warms up the duration of on time drops down. Its the suggested setup for the 654 and a non dedicated boiler

CBRob

 My local rep is repmaster in Denver. You guys heard of them?

Shamrock doesn't come this far west. 

Zman

Shamrock is the rep for Tekmar but not other Watts products. I talk with them on a regular basis. They also rep Lochivar and the residential Taco products.

Mike_Breault

@CBRob sorry for the delay I was camping the past week and a half.... oversizing wont "hurt" bu thte easiest way I see to explain it would be to say that the HE is your heat source, heated by your boiler, you will need the energy to it to get the out put.. if you need 100k, up to 20% larger is fine, your boiler still has to feed it and there is a bit of a loss.

Repmaster is a good group too

@Zman is right, best first contact is your local rep for design assistance. and we support them, this gives you local boots as it were.

Best