Simple/Reliable design with a single loop, ECM pump, rads with TRVs and PBV?

gdirwin

Most hydronic designs I see use P/S loops with 2 or more pumps.

Can anyone tell me what is wrong (if anything) with the following:
- electric boiler

- single loop design with 1 ECM pump

- short/fat manifolds (on supply and return) with numerous 1/2 pex feeds to radiators (inc balancing valves)

- TRVs on each rad

- PBV (pressure bypass valve) between supply and return (to ensure min flow in the boiler is met)

This seems much simpler than other designs:
- only 1 pump (spend money saved on a redundant pump).

- use of simple/inexpensive/reliable TRV on each rad ( vs zone valves or circulators)

- no need for expensive LLH or hydraulic separator

Other stuff of course is still required (expansion tank, pressure relief, fill valves, air separator, dirtmag, gauges etc...).


Are their any ECM pumps that can be programmed for constant pressure operation (so they throttle down as zones meet demand and close) but with a minimum flow constraint?  

If the TRV is left off one rad (same room with a main thermostat) would this help guarantee min flow to meet boiler requirements?

Are electric boilers less prone to thermal shock (ie a plug of cold fluid injected if a  zone is opened)?

All help appreciated...

hot_rod

Sounds sounds like a good plan. The P/S or Sep is mainly for boilers with high pressure drop, so they get a dedicated, correct circ pump

Or to seperate circs if of different sizes and capacities, common in some large commercial applications.

As long as it is a wide open boiler, not a tankless electric 👮‍♀️

I would encourage a good air purger and a mag Sep to protect the ECM and TRVs. 

No problem with return protection or minimum boiler flow, use a boiler that can modulate the elements, Thermo 2000 makes some nice, small modulating boilers, other brands do.

Jamie Hall

Nothing much wrong with the fundamental concept. You have hit on the basic problem of a single pump type operation with zoning -- either in groups or at the radiation with TRVs -- how do you maintain a minimum flow through the boiler? -- and there is no simple way to do that; a pressure relief bypass, as you suggest, is probably the best approach (it's used in hydraulic systems all the time, after all! Though at a slightly higher pressure...).

You have also mentioned sort of as an aside the problem of the main boiler control. A main thermostat in one space is very problematic, as the entire system is dependent on that one thermostat wanting heat when any zone anywhere wants heat -- a somewhat dubious control assumption.

Electric boilers are, as a whole, pretty good about handling widely and quickly varying feedwater temperatures. You do want to do your numbers, however. In many areas of North America they are by far the most expensive way to heat water you can find. If you are at the same time environmentally inclined, they are also the most carbon intensive approach available. On the whole, a dubious choice unless you have to have one for some reason.

Paul Pollets

This is a good way to go. Hopefully, your electricity is "affordable". It's $.12/Kwhr in Seattle, so electric boilers are common. I've used the modulating models that work well. A 40amp power supply is usually a minimum requirement. I use an Alpha pump and size the radiators for 140 degrees rather than 180. Like Hot Rod said, a good dirt/mag separator and air purger should be part of the piping.

gdirwin

Thank you hot_rod and Jamie - your help is appreciated.

I choose electric as it is for a cottage on an island - no NG. Propane is an option, but extra complexities to get it filled by barge (or on winter ice roads), plus a big pig needed, venting etc. Electricity is expensive (Ontario Canada) but I plan to reduce long term costs by installing solar panels on roof. Also have a kick-**** wood stove (Blaze King) so will use for the bulk heating when we are there. Want room by room zoning to heat some rooms that are far away from the wood stove (and to keep some rooms closed off when they are not used) - TRVs are a more reliable way compared to zone valves I think.

The main thermostat will mostly be a remote on/off switch (smart wifi thermostat so I can turn on remotely and monitor the temps) - ie temperature setpoints will be done on the TRVs. I may setup the central thermostat in the coldest part of the cottage (shop) - if i set this to a low temp (say 10degC) it will keep the cottage above freezing (ie standby mode).

It would be great if there was a way of coordinating the TRVs so that they could all be lowered together (ie smart TRVs) - not woth the complexity though and will keep it simple.

I will do some more research on the electric boiler (CEBR-24 made locally by Lion/Concept) - I know it modulates each stage of heating elements using relays (and has an outdoor temp reset curve) but will need to contact the supplier to determine min flow requirements.

Any advice on what pressure bypass valve to buy, and the method used to set it? Ideally this would be completely closed until main loop flow gets to the boiler minimum (and then would modulate open to keep this minimum flow) - it likely will be set by pressure differential however. Not sure how to coordinate this with the Pressure/flow algorithms in the ECM pump (likely an Alpha 2). Any more advice on this?

Thanks (in advance),

hot_rod

A simple paddle flow switch would assure the boiler is not firing with no flow. Nico at T 2000 tells me no flow operation depends on the KW size of the boiler selection.

Here is a good cost calculator
https://coalpail.com/fuel-comparison-calculator-home-heating

I pay .11KWh for 8 months of the year, Lp at 3.79 currently, so electric it is until I get NG. LP was 1.99 when I left Missouri. It's a very wide price range on LP.

I've always wanted to try one of these "shoe box" ground loop heat pumps for an application like that. You have plenty of heat sink surrounding you.

https://www.kensaheatpumps.com/shoebox-ground-source-heat-pump/

Jamie Hall

Cottage country?

In the application which you describe, I personally would run electric baseboards and get rid of the complication of pipes and TRVs and freezing and all that sort of thing entirely. You will use almost exactly the same amount of power -- perhaps slightly less -- as you would with an electric boiler. Each room could have its own line voltage thermostat, or you could control one or more spaces with a wi-fi thermostat controlling a contactor (big relay) which in turn controls the baseboards.

The other obvious question is... do you, in fact, have enough power? Remember that 1 kilowatt -- 5 amps at 240 volts -- is only about 3500 BTUh. Unless your cottage is remarkably well insulated, I would be kind of surprised if you could get away with much less than 10 KW on the colder days...

hot_rod

Electric panel radiators are another option as you see get some "radiant" heat from them, compared to electric baseboard. Towel warmer in the bath. Electric radiant mats also.

Unless you plan on a heat pump to get up in to the 3 COP, with electricity as the fuel source, Jamies idea makes sense and saves cents.

Rich_49

You really won't need a PDBV in any system with an ecm . That was really equipment for zoned systems with a PSC circ . Using one nowadays is akin to using a band aid for a self inflicted sucking chest wound .
Parallel circuits to radiators will give you whatever flow x how many circuits if your math is done properly . The chances of having less than minimum flow are slim .

The unit you mention is a monster , how big is this cottage ? How many radiators



https://www.conceptmfginc.com/content/brochures/CEBR Manual.pdf

Jamie Hall

Rich_49 said:

You really won't need a PDBV in any system with an ecm . That was really equipment for zoned systems with a PSC circ . Using one nowadays is akin to using a band aid for a self inflicted sucking chest wound .
Parallel circuits to radiators will give you whatever flow x how many circuits if your math is done properly . The chances of having less than minimum flow are slim .

The unit you mention is a monster , how big is this cottage ? How many radiators



https://www.conceptmfginc.com/content/brochures/CEBR Manual.pdf

Which brings me back to my comment above: do you, in fact, have enough power at your cabin? That boiler takes 100 amperes at 240 volts. To run it at all, you will need your service entrance to be at least 150 ampere 240 volt, and I would be willing to say that Ontario Hydro is going to want you to be wired for 200 amps. Are you?

I also note that the unit is NOT designed to be used with a power stealing or parasitic type thermostat. Not that you can't use a separate wi-fi thermostat, but it will need its own power supply and it will need to control this unit through a relay.

gdirwin

200A main panel and can handle the 100A for the boiler.

Total 3000 sq ft but lower story is a shop that will be heated to a lower temperature, 12 feeds of 1/2 pex to the radiators.  I did heat load calcs and boiler is adequate.

Thought about simple electric baseboards but hard to control them all remotely - ie prefer boiler, glycol and hydronic rads.

My concern with a 1 loop design is still min flow to the boiler if all TRVs shut off.  Concept got back to me asap - min flow of 5 GPM is required.

Could use traditional P/S 2 loop design, but means a 2nd pump (not a huge deal).

Am looking for a device (PDBV?) which will always allow some flow between supply and return so ECM pump always provides a min flow in a simple 1 loop design.   

Jamie Hall

"Thought about simple electric baseboards but hard to control them all remotely - ie prefer boiler, glycol and hydronic rads." Well, no. There is no reason why the circuit or circuits powering the straight electric baseboards can't be controlled by a contactor which, in turn, is controlled remotely -- by wi-fi or whatever. If Alexa or whoever can turn a light on or off remotely -- which I believe is possible -- it is no more difficult to control a much larger circuit. Just a different relay.

Providing a minimum flow rate in an hydraulic system -- which is basically what we are looking at here -- requires a bypass. In power hydraulics, this is opened by a pressure relief valve, but that really isn't an option here as the margin -- for any common circulating pump you might use -- is just too small for reliable control. You will find it far more satisfactory and reliable to use primary/secondary piping. This does not eliminate the rather curious problem of how to shut the boiler off when no zones are calling at all. Not that you have to, but it is a bit wasteful to leave it running (actually not as bad as it might be -- it will run very little when there is no heating load), although both circulators will be running; the secondary dead headed, which isn't wonderful but won't hurt it much.

One thing I haven't mentioned: you absolutely must use antifreeze in your system. The power will go out from time to time, and that means that the system will drop below freezing from time to time.

Rich_49

I thought you were using a manifold with 1/2" homeruns to each radiator . Why are you now mentioning a 1 loop design , what am I missing ? I believed that you would use a thermostat in each floor as a high limit and use the TRVs as they were intended , with the TRV controlling flow rates and individual radiators . You also mentioned using ECM circ , with an ECM circ a pressure differential bypass valve is quite unnecessary as I described before , you really don't need one in a system with a variable speed circ ( ECM) . The thermostats act like high limits , located in the coldest room and set to a temp that is what you deem too hot . If that room gets that warm the boiler shuts down , so does the circ if both stats reach setpoint . No boiler , no flow , no problem

hot_rod

P/S or better yet a hydraulic sep is how you will assure that 5 gpm flow. I'm not sure what type of small electric boiler needs that kind of minimum flow? Is it a tankless water heater? 5 gpm sounds like enough flow for design condition.

hot_rod

This boiler?

gdirwin

The boiler is CEBR-24 here:
https://www.conceptmfginc.com/content/brochures/CEBR Manual.pdf

This is not an instantaneous water heater, but is a dedicated boiler. I think you are right about the min flow of 5 GPM - this is probably when all elements are on, and not the min flow required when the boiler has throttled down with only 1 element on.

The simple design I was hoping to use is a single boiler loop (ie not P/S) - ie 1 pump in the boiler supply pipe, going to a supply manifold, 12 zones of radiators with TRVs, return manifold, back into the boiler. The key problem is that if all rad TRVs close, then there is no flow in the boiler loop. The PDBV (direct between supply and return) was proposed to ensure the boiler always has the flow required. Sorry if I get the standard terms wrong (not a single loop in the sense of the rads with bypass valves etc)...

Jamie - as you said, electric baseboards could be used with relays/contactors, fed from thermostats in each room, and perhaps coordinated with a central on/off remote switch or smart central thermostat. This would require numerous breaker slots (12 zones, but >16 rads double pole breakers) and my panel does not have that much room (so would have to add another sub-panel). Amp draw would be the similar - still prefer the central boiler (and yes I have glycol in case of a loss of power - 40% as it is cold up here!).


What I have concluded (based on all the help on this forum) that I should stick to a traditional P/S boiler loop design with 2 pumps (one primary fixed speed and an ECM variable speed secondary pump). The concept of trying to do it all with a single pump is possible, but would require careful coordination of the PDBV setting with the ECM pump algorithms. Ie changing the pump settings would probably require adjustment of the PDBV - ie no longer simple.

P/S de-couples the radiator and boiler requirements, and the cost of another pump in the primary is worth it to keep it simple/traditional. As Jamie mentioned, I also have to design it to turn the system off at some point (perhaps a low-flow meter/switch in the secondary loop or a master thermostat) - an extra step compared to using zone valves (but overall the use of TRVs seems to be more reliable/simple compared to using 12 zone valves). The ECM pump can be dead-headed in the secondary, but still best to turn it all off at some point.

Got a plan, and thank you to all who responded! Greatly helps to have experienced folks to work through the options.
Garth

hot_rod

Your P/S piping plan will work fine. I am a fan of TRV control logic

I am almost certain it could be piped like their drawing but with TRVs instead of zone valves and work fine, direct pipe. I checked with another electric boiler manufacturer that looks identical to that one and they are comfortable with no flow on smaller element systems.

If it modulated down to a single element with no flow it should just reach the temperature limit you have set on the boiler and shutdown. It may over-shoot a few degrees.

I built my own electric boiler, of sorts It holds less than 1 gallon of water, has a 5500W element when flow stops the element reaches setpoint quickly and shuts off.

I have it wired with a relay now so it only heats when the pump is running, a flow switch could also be used to start the boiler only when it sees a minimum flow, down to .5 gpm even.

So a TRV cracks open, the delta P circulator moves flow, a flow switch sees that flow and enables the boiler call for heat.

Flow switches are common as a safety turn off also. If flow stops on many low mass boilers, and copper tube type water heaters for example.