How Does The Constant Flow Thing Work?

[velvetfoot]

My current oil system is typical: a thermostat calls for heat, a circulator starts, hot water is circulated through the baseboards,the burner comes on when the aquastat temp drops to a certain level. The pellet boiler I ordered can modulate down to 30%, and I didn't oversize it. I can see fewer stops and starts being an advantage and the potential for a more constant room temperature. I've read about it but can't recall. How is this done? I know it could be a dumb question, and I'll do some more reading. Thanks.

 

[__dan]

With outside air temp (OAT) hot water reset of the load loops. Vary the load loop temp with OAT reset, the load stays on longer at a lower temp and the boiler, if it has turndown, may dial in to the load. The load is not doing start stop and the boiler may modulate down and dial in to the load. IMO, this one feature, while expensive to add, may have a great gain in efficiency especially on low load days, and the benefit of reducing on/off firing cycles for the pellet burner.

Variable speed OAT reset injection pump controllers in the photos.

https://www.hearth.com/talk/attachments/p1000718-jpg.87975/

https://www.hearth.com/talk/attachments/p1000703-jpg.87979/

 

[velvetfoot]

Great. Thanks for taking the time.

 

[heaterman]

Or....Install TRV's on your baseboard, install a VS pump and just tie a thermostat to the pellet boiler to initiate a call for heat.
You baseboard will now be constant but variable output which is exact how the Euro's design their boilers to deliver maximum efficiency.

 

[Downeast Farmer]

Or....Install TRV's on your baseboard, install a VS pump and just tie a thermostat to the pellet boiler to initiate a call for heat.
You baseboard will now be constant but variable output which is exact how the Euro's design their boilers to deliver maximum efficiency.

Would you follow the same strategy for staple-up radiant floor?

 

[velvetfoot]

Or....Install TRV's on your baseboard, install a VS pump and just tie a thermostat to the pellet boiler to initiate a call for heat.
You baseboard will now be constant but variable output which is exact how the Euro's design their boilers to deliver maximum efficiency.

Why would you necessarily need TRVs if you just put the whole zone on a VS pump? A serially piped zone would require a lot of rework.

How is the speed of the VS pump controlled? When the thermostat calls for heat, what changes the speed of the VS pump?

 

[arbutus]

To answer the title of your post: It works GREAT!

Why would you necessarily need TRVs if you just put the whole zone on a VS pump? A serially piped zone would require a lot of rework.

How is the speed of the VS pump controlled? When the thermostat calls for heat, what changes the speed of the VS pump?

There are multiple ways to achieve the same effect.
If you used TRVs you would need to use a pressure sensing pump like a Grundfos Alpha.
Or, you could use a Taco Bumblebee or similar that changes speed to meet a set temperature differential without replumbing your serial baseboard.
Or you could plumb in a 3 or 4 way mixing valve with outdoor reset to temper the water in your zone based on outdoor temperature.

Would you follow the same strategy for staple-up radiant floor?

I used a Taco i series 3 way with outdoor reset. There are many others.

 

[velvetfoot]

Or, you could use a Taco Bumblebee or similar that changes speed to meet a set temperature differential without replumbing your serial baseboard.

How does that work to maintain a zone's temperature?

 

[heaterman]

How does that work to maintain a zone's temperature?

The issue I'm thinking about is keeping that boiler from cycling of/off and maintaining room temp.
The actual water temp in the zone will for the most part be regulated by the TRV. With it's ability to "throttle" the heat, a TRV system will squeeze flow down until you have a huge temp drop across the zone. You can call the pump on with a single room thermostat somewhere in the house (via a relay of course) and let the TRV's "watch" the zone temp.

No mix valves, no electronics, very simple. The radiator in my living room will show anywhere from a 10-15* drop all the way out to 60-70* (170 EWT and 100* or even less LWT.

.......just went and checked the # of cycles on my BioWin vs hours run. 967 starts in 4158 hours which gives an average run time of over 4 hours per cycle. That is what you want to shoot for. No sense having a modulating burner connected to an on/off load.

 

[heaterman]

Would you follow the same strategy for staple-up radiant floor?

No reason you could not do that. There are even TRV's that work off a floor sensor (remote bulb).

 

[heaterman]

Why would you necessarily need TRVs if you just put the whole zone on a VS pump? A serially piped zone would require a lot of rework.

How is the speed of the VS pump controlled? When the thermostat calls for heat, what changes the speed of the VS pump?

The VS pump will control itself based on how much flow the TRV's are calling for as they modulate open and closed.

There are limits to how you can use a system of this type and having all the emitters piped in series is one of them. If however the house is piped into multiple zones it would work great. The idea is to keep the pump on so you have constant flow along with a constant call for heat. Then when you factor in the ability of the TRV's to vary or modulate that flow, the boiler can ramp up and down to meet demand.

 

[maple1]

Help me with something simple re. TRVs - do they open & close real slow? Do they maintain part-openings for periods of time? i.e., as opposed to zone valves, which are quickly open & shut?

This one has me thinking maybe I should replace my zone valves with TRVs - but is that as straightforward as it sounds? Thinking there must be more to it and it wouldn't be a simple swap?

 

[velvetfoot]

For me, with two serial zones on circulators, I wonder if I could replace the pumps with variable speed and they could change flow instead of go on and off.

I'm with you maple; I don't get it.

The TRVs are modulating the flow in response to room temperature and the variable speed pump is modulating in response to temperature or flow?

I can see the scenario where you have individual rooms, let's say, on a panel radiator or two. The flow through the rads and back to the (boiler) would be controlled by the trv. There'd have to be a way to get each little zone's water back to the boiler or to a parallel header. I can't see why the entire zone can't be controlled that way, baseboard emitters or not.

So there could be a temp sensor upstairs in one of the serial zones and another in the downstairs zones and they could be connected to TRVs in the basement and that could control the rooms's temperature by varying the flow and the pump could vary its speed in response. Could that be it?

 

[DZL_Damon]

I thought TRV's were 3 way valves that would allow more/less flow to your radiator. Most TRV's sense air temperature flowing up to the radiator... when they get hot they throttle flow to the radiator and bypass more. Inversely they will flow more to the radiator when it's cooler in the room.

I think the Bumblebee does the same thing but it measures dT across the water temp which should be proportional to room temperature. If dT is set at 20*F, it needs to pump more if it's cold upstairs because the baseboard/radiators are pulling in colder air from the room and putting out more btu's. However, I'd think the TRV's would be more accurate with this with a smaller temperature variation in the room? I don't know personally since I have neither, but will in my next house.

 

[maple1]

Before finding this place, I was never really aware of anything besides ordinary zone valves & circ pumps.

I replaced my 3 speed with an Alpha, which was a big improvement on its own with the zone valves I have. But now I'm thinking more improvements could be made in looking at my zone valve situation. It would be nice to replace the sudden start/stop nature of the zone valves with constant variable circulation, if that could be done by a simple replacement of the zone valves with something better, if simple replacement is possible - since I already now have in place the VS pump.

Just enough knowledge to be dangerous....

 

[heaterman]

Here's a real quick drawing that shows the basic principle and components.

 

[arbutus]

How does that work to maintain a zone's temperature?

Thinking more about it, it won't if you have a constant water temperature. You need a controller to tell the pump to speed up or slow down in response to room temp, rather than water temp differential. I'm not sure if anyone makes something like that or not, and as Heaterman pointed out it wouldn't be ideal for a long serial run of baseboard because you would have extreme water temperatures.

Help me with something simple re. TRVs - do they open & close real slow? Do they maintain part-openings for periods of time? i.e., as opposed to zone valves, which are quickly open & shut?

This one has me thinking maybe I should replace my zone valves with TRVs - but is that as straightforward as it sounds? Thinking there must be more to it and it wouldn't be a simple swap?

I'm only familiar with these for panel radiators: http://www.pexsupply.com/Buderus-82721124-Oventrop-Radiator-Sensor-Head
They adjust slowly in response to air temperature changes - over the course of several minutes - and do not completely close when heat is needed in the room.