Heating with Thermal Storage and Low Flow Temps

[JohnDolz]

Thanks for this confirmation - that is what I surmised. Regarding the high efficiencies of condensing boilers, this is basically due to the capture of the latent heat in the flue gas as it condenses to liquid, and the low return temperatures are what makes this possible. Then, ODR with a mixing valve and flow control provides benefits in maintaining the storage tank thermocline, which I can easily buy into as well.


That's pretty much my thoughts. I'm lucky that I can design from the ground up and don't have to work with an existing system (i.e. fin-tube radiators), which would restrict my strategies somewhat and may require more complex control schemes.


Yeah, me too. But I can believe that it can save money in some cases. For instance, my cast iron radiator system has two zones, and one of the thermostats turns on at set temperature and off at set temperature +4 degrees. If the temperature is warm, the cast iron radiators will take a while to heat up, and then once the temperature heat +4 degrees, and the boiler goes off, the room temperature will keep rising if the outdoor temperature is not too high. ODR senses that and keeps the boiler water output temperature lower to prevent unnecessary overshoot and unnecessary heating.

You are both way beyond my knowledge level so I will leave the conversation to the 2 of you. In my case, when my propane boiler kicks in I have an electric valve that isolates my thermal storage and my the propane boiler just provides low temp water directly to the heating zones. The ODR in the propane boiler tells the propane boiler what the target is for the Supply water. I programmed it with basically the same heat curve that I use for my thermal storage which created a new challenge. Since my supply target was so close to the return temp I had the boiler cycling on and off almost every minute. It was mild outside so maybe I just need to pull the end points of my heat curve in for the hotter days. I adjusted the programming so that there is a minimum of 5 minutes between firings - the thought is this will cause return temp to drop. I haven't tested it now that it is colder, too lazy and too cheap to burn the propane.

 

[velvetfoot]

I have an electric valve that isolates my thermal storage

Could you go into a little more detail? eg, normally open, motor vs solenoid, make/model, etc?

I do understand you are indeed getting max efficiency by operating your mod/con boiler in the condensing zone. It does modulate, right?

 

[JohnDolz]

Thanks for this confirmation - that is what I surmised. Regarding the high efficiencies of condensing boilers, this is basically due to the capture of the latent heat in the flue gas as it condenses to liquid, and the low return temperatures are what makes this possible. Then, ODR with a mixing valve and flow control provides benefits in maintaining the storage tank thermocline, which I can easily buy into as well.


That's pretty much my thoughts. I'm lucky that I can design from the ground up and don't have to work with an existing system (i.e. fin-tube radiators), which would restrict my strategies somewhat and may require more complex control schemes.


Yeah, me too. But I can believe that it can save money in some cases. For instance, my cast iron radiator system has two zones, and one of the thermostats turns on at set temperature and off at set temperature +4 degrees. If the temperature is warm, the cast iron radiators will take a while to heat up, and then once the temperature heat +4 degrees, and the boiler goes off, the room temperature will keep rising if the outdoor temperature is not too high. ODR senses that and keeps the boiler water output temperature lower to prevent unnecessary overshoot and unnecessary heating.

You are both way beyond my knowledge level so I will leave the conversation to the 2 of you. In my case, when my propane boiler kicks in I have an electric valve that isolates my thermal storage and my the propane boiler just provides low temp water directly to the heating zones. The ODR in the propane boiler tells the propane boiler what the target is for the Supply water. I programmed it with basically the same heat curve that I use for my thermal storage which created a new challenge. Since my supply target was so close to the return temp I had the boiler cycling on and off almost every minute. It was mild outside so maybe I just need to pull the end points of my heat curve in for the hotter days. I adjusted the programming so that there is a minimum of 5 minutes between firings - the thought is this will cause return temp to drop. I haven't tested it now that it is colder, too lazy and too cheap to burn the propane.

Could you go into a little more detail? eg, normally open, motor vs solenoid, make/model, etc?

I do understand you are indeed getting max efficiency by operating your mod/con boiler in the condensing zone. It does modulate, right?

Yes, it modulates. The valve is normally open. I will take some pics later tonight, I don't know much about it - last year I was enjoying someone else doing it all for me. This year I have been forced into the drivers seat. The reason I have it is because I was getting supply water from the propane boiler feeding into my tanks through the return line. Based on what I have been reading it probably should have been engineered a little different. I may need to quit this forum before I rip everything out, baseboard emitters included, and start from scratch.

 

[JohnDolz]

Could you go into a little more detail? eg, normally open, motor vs solenoid, make/model, etc?

I do understand you are indeed getting max efficiency by operating your mod/con boiler in the condensing zone. It does modulate, right?

See photos, hope they help.

 

[TCaldwell]

You are both way beyond my knowledge level so I will leave the conversation to the 2 of you. In my case, when my propane boiler kicks in I have an electric valve that isolates my thermal storage and my the propane boiler just provides low temp water directly to the heating zones. The ODR in the propane boiler tells the propane boiler what the target is for the Supply water. I programmed it with basically the same heat curve that I use for my thermal storage which created a new challenge. Since my supply target was so close to the return temp I had the boiler cycling on and off almost every minute. It was mild outside so maybe I just need to pull the end points of my heat curve in for the hotter days. I adjusted the programming so that there is a minimum of 5 minutes between firings - the thought is this will cause return temp to drop. I haven't tested it now that it is colder, too lazy and too cheap to burn the propane.

Yes, it modulates. The valve is normally open. I will take some pics later tonight, I don't know much about it - last year I was enjoying someone else doing it all for me. This year I have been forced into the drivers seat. The reason I have it is because I was getting supply water from the propane boiler feeding into my tanks through the return line. Based on what I have been reading it probably should have been engineered a little different. I may need to quit this forum before I rip everything out, baseboard emitters included, and start from scratch.

Has the drawn line move already?

 

[JohnDolz]

Has the drawn line move already?

In studying my past behavior I find that I need to complete the things on my list before I move the line. For now I have been educated on the need for air intake and then I have some plumbing that needs to be done. Luckily I lined up an expert technician so I expect these items to be knocked out in no time.

 

[cpeltier]

I built a timber frame with sip panels and it should be sealed up tighter than a popcorn fart, but when the wind howls it seems to come right through the walls, all my big windows probably don't help either

I built an almost net-zero house half way up a 4000' mountain in Vermont and just returned so I'm late to this thread. My mountain house is also built with SIP panels, ICF foundation, and Marvin Integrity (good but not high end) windows. My house is very tight and it's 100% radiant, no baseboard or fan coil. This house uses a 1st generation NoFossil control system as a starting point. I completely rewrote it for my use (added One Wire sensors and PWM/PID for Zone control) and it works well but is a totally custom one-off system (which I don't like). It's a standing column GeoThermal Water-to-water heat pump with a backup or stage 2 ModCon LP boiler. My design temperature using Outdoor reset is 115F @ -25F. My SIP panels were foamed at the joints and the house is very tight. So tight in fact that if I turn on my kitchen fan it will suck the fire out of the fireplace. I walked around the house with a FLIR and fixed many gaps. I still have a few outstanding which the Cluster flies have found.
http://mirabal.netcarrier.com:84/cgi-bin/statuscgi

 

[JohnDolz]

I built an almost net-zero house half way up a 4000' mountain in Vermont and just returned so I'm late to this thread. My mountain house is also built with SIP panels, ICF foundation, and Marvin Integrity (good but not high end) windows. My house is very tight and it's 100% radiant, no baseboard or fan coil. This house uses a 1st generation NoFossil control system as a starting point. I completely rewrote it for my use (added One Wire sensors and PWM/PID for Zone control) and it works well but is a totally custom one-off system (which I don't like). It's a standing column GeoThermal Water-to-water heat pump with a backup or stage 2 ModCon LP boiler. My design temperature using Outdoor reset is 115F @ -25F. My SIP panels were foamed at the joints and the house is very tight. So tight in fact that if I turn on my kitchen fan it will suck the fire out of the fireplace. I walked around the house with a FLIR and fixed many gaps. I still have a few outstanding which the Cluster flies have found.
http://mirabal.netcarrier.com:84/cgi-bin/statuscgi

Funny about a million years ago I interviewed with a company that (if I recall correctly) had the patent on closed loop Geothermal, still surprised that it never took off as a concept. Question for you on your LP boiler, with the design temp so low do you have any issues with it firing on and off? I mentioned it somewhere in this thread but when I tried that I had my boiler firing on and off almost every minute because the return temp was so close to Design temp. That was a fairly warm day. Since then I also adjusted the programming in the boiler so it has a minimum of 5 minutes between firings. I've been too lazy to test it again to see if this creates more of a constant firing at low temp. Have you seen this issue? If so how did you address it? Thanks.

 

[cpeltier]

Funny about a million years ago I interviewed with a company that (if I recall correctly) had the patent on closed loop Geothermal, still surprised that it never took off as a concept. Question for you on your LP boiler, with the design temp so low do you have any issues with it firing on and off? I mentioned it somewhere in this thread but when I tried that I had my boiler firing on and off almost every minute because the return temp was so close to Design temp. That was a fairly warm day. Since then I also adjusted the programming in the boiler so it has a minimum of 5 minutes between firings. I've been too lazy to test it again to see if this creates more of a constant firing at low temp. Have you seen this issue? If so how did you address it? Thanks.

This system went live in 2009/2010 season so I had to deal with technology available at that time. My ModCon did not have Modbus control and I didn't want to have to directly control the modulation rate of the boiler as I had a fault tolerant backup mode that took my fancy control system out of the equation if a fault was detected (unoccupied home in a harsh environment). I programmed the LP ModCon (Triangle tube, 4-1 turndown ratio) with an ODR curve that matches my control system. My control system would generate a boiler demand if the heat pump could not keep up but it was very stingy in its operation as it's primarily a solar powered (grid tied) house. I had the zones split up into 4 groups and each group would synchronize on a time interval with a PWM cycle designed to minimize overlap as I was pushing the limits of a 5 ton heat pump on a 3500 square foot structure in that environment. There are no thermostats, just OneWire sensors embedded in the drywall in each zone. The control system would adjust the target water temperatures based on the hottest desired room temperature. The PWM mechanism would take care of the rest. The system or LP boiler doesn't short cycle. It works very well. The key to my system is in the programming of the control system; PWM for zone control, and having the thermostats embedded in the control system so I know what the desired room temperature is allowing me to run the coldest system water temperatures possible. Running the coldest water possible is key to getting the highest system efficiency and becomes paramount when using a Heat Pump as your hot water source. The heat pump won't generate water hotter then 115F anyway and it's COP is also very poor at this limit. I designed my radiant heating system based on this fact and all of the loops were sized according to this low design temperature.

 

[JohnDolz]

This system went live in 2009/2010 season so I had to deal with technology available at that time. My ModCon did not have Modbus control and I didn't want to have to directly control the modulation rate of the boiler as I had a fault tolerant backup mode that took my fancy control system out of the equation if a fault was detected (unoccupied home in a harsh environment). I programmed the LP ModCon (Triangle tube, 4-1 turndown ratio) with an ODR curve that matches my control system. My control system would generate a boiler demand if the heat pump could not keep up but it was very stingy in its operation as it's primarily a solar powered (grid tied) house. I had the zones split up into 4 groups and each group would synchronize on a time interval with a PWM cycle designed to minimize overlap as I was pushing the limits of a 5 ton heat pump on a 3500 square foot structure in that environment. There are no thermostats, just OneWire sensors embedded in the drywall in each zone. The control system would adjust the target water temperatures based on the hottest desired room temperature. The PWM mechanism would take care of the rest. The system or LP boiler doesn't short cycle. It works very well. The key to my system is in the programming of the control system; PWM for zone control, and having the thermostats embedded in the control system so I know what the desired room temperature is allowing me to run the coldest system water temperatures possible. Running the coldest water possible is key to getting the highest system efficiency and becomes paramount when using a Heat Pump as your hot water source. The heat pump won't generate water hotter then 115F anyway and it's COP is also very poor at this limit. I designed my radiant heating system based on this fact and all of the loops were sized according to this low design temperature.

Thanks, I have a Triangle Tube, installed around 2011. I believe mine was the first generation with the ODR tied into he heatcurve. I say this because this year I finally learned a few things about it, including the fact that it was reading the wrong outdoor temp. In exploring this I learned I had he 1st generation software/display module. They sent me an updated one which I installed a few weeks ago. How did you avoid the short cycle? or is it simply the fact that it is so cold up there that return temp differential is always great enough to avoid this (spent many years skiing at Killington so I understand it is a bit chillier than here in CT).

 

[cpeltier]

Thanks, I have a Triangle Tube, installed around 2011. I believe mine was the first generation with the ODR tied into he heatcurve. I say this because this year I finally learned a few things about it, including the fact that it was reading the wrong outdoor temp. In exploring this I learned I had he 1st generation software/display module. They sent me an updated one which I installed a few weeks ago. How did you avoid the short cycle? or is it simply the fact that it is so cold up there that return temp differential is always great enough to avoid this (spent many years skiing at Killington so I understand it is a bit chillier than here in CT).

Mine is the Triangle Tube Prestige 175 KBTU with the Honeywell MCBA control module. It will short cycle if the load is less then it's maximum turn-down. For me it's around 35 KBTU/hr Input when that happens. I haven't really noticed it as the second stage almost never runs except when it's generating DHW. It's a ski house on Lincoln Peak at Sugarbush. The DHW is on the ModCon because when the 10 people come back from skiing they all take a shower at once! I do have a desuper coil in the DHW tank which does the initial heat up and keeps it topped off. I'd like to know more about this updated MCBA module!

 

[JohnDolz]

Mine is the Triangle Tube Prestige 175 KBTU with the Honeywell MCBA control module. It will short cycle if the load is less then it's maximum turn-down. For me it's around 35 KBTU/hr Input when that happens. I haven't really noticed it as the second stage almost never runs except when it's generating DHW. It's a ski house on Lincoln Peak at Sugarbush. The DHW is on the ModCon because when the 10 people come back from skiing they all take a shower at once! I do have a desuper coil in the DHW tank which does the initial heat up and keeps it topped off. I'd like to know more about this updated MCBA module!

Can I bribe you to stop by on your way to Sugarbush? You can have the best Cappuccino you have ever had. Not quite sure what Control Module I have. I know when I asked about adjusting the outdoor temp (I was talking to the engineer at Triangle) he asked me what version software it was, from there he determined I was on the old version and sent me out a new module to install. The outdoor temp then matched what I was getting on my Effecta ODR. Their warranty department is supposed to handle this, if you give them a call I am sure they can walk you through it. Just for more laughs my plumber installed the ODR on the east side of my house under the boiler exhaust. Want to guess how well things worked when it was set to ODR mode? You can message me as well, happy to give you my phone # and check anything you like. I am heading out of town tomorrow early AM so this is a tough week.

 

[JohnDolz]

Mine is the Triangle Tube Prestige 175 KBTU with the Honeywell MCBA control module. It will short cycle if the load is less then it's maximum turn-down. For me it's around 35 KBTU/hr Input when that happens. I haven't really noticed it as the second stage almost never runs except when it's generating DHW. It's a ski house on Lincoln Peak at Sugarbush. The DHW is on the ModCon because when the 10 people come back from skiing they all take a shower at once! I do have a desuper coil in the DHW tank which does the initial heat up and keeps it topped off. I'd like to know more about this updated MCBA module!

Since you get me thinking and since I am leaving for the week I thought I would test my backup system. I find that even with it being reasonably cold today and windy I think I may have a challenge with short cycle (not sure what a good time between cycles really is, any idea?). The design temp is 114 today, when I run my thermal storage system my design and return temps are almost identical. I turned of the thermal to test the propane and of course the firing shut down almost instant (CH Demand temp met). Since I programmed the minimum time between firing to 5 minutes my circulators ran for a while dropping the return temp. Next time my boiler fired it fired for at least a few minutes before the return temp climbed enough that CH Demand Temp was met. I have a Modine Hydronic heater that is running in the basement, I know that returns really cold water - point is that if I had that shut off (which I prefer due to the noise) I would bet my return temps would return to supply temp very quickly. Wondering how you get around this? Maybe the answer is just knowing what an acceptable # of cycles per day is. I am going to let this run for an hour or wo and see if I maintain hose temps or not. Any insight is appreciated!

 

[TCaldwell]

John,
Possibly Cpeltier's radiant return temps are low enough for a sustained time allowing his boiler not to cycle? I think with fin tube or any other low mass emitter running properly on odr(as yours does), pretty much constant flow with tight supply and return delta would induce cycling. Can you limit the firing rate of the boiler? I dunno

 

[JohnDolz]

John,
Possibly Cpeltier's radiant return temps are low enough for a sustained time allowing his boiler not to cycle? I think with fin tube or any other low mass emitter running properly on odr(as yours does), pretty much constant flow with tight supply and return delta would induce cycling. Can you limit the firing rate of the boiler? I dunno

Thanks. I do have the ability to control the minimum time between firings. I sent Triangle Tube an email earlier today asking what target I should be shooting for, hard to hit the bulls-eye if you don't know where it is or what it looks like. I haven't paid any attention to it as I really haven't used it since I fired up the wood boiler but I am going away this week and with it being so cold I thought I better make sure my backup system would actually do something. It seems to work fine and kept me at a cozy 72. The question is around the # of firings and whether or not I am cutting into the longevity of the boiler.

 

[Boardroom]

I've been following various threads in this topic and my main question has been whether John's system is just one result that could be obtained or if another, equivalent result could be obtained through the following:

1. Install TRVs on cast iron radiators that have sufficient size to heat at water temperatures in the 100-120 degree F range (120 degrees needed for a 0 degree outdoor day, 100 degrees ok for a 40 degree outdoor day)
2. Install a constant pressure pump to circulate water from boiler storage
3. Charge storage when water temps are ~100 degrees F up to ~180 degrees F

That seems to be Maple1's approach, and simpler with less control complexity and "things that can go wrong". What am I missing?

OK. I have been following this thread and must admit John that I am guilty as you were of thinking that I need very hot water to heat my house. There is no way that my drafty late 1800's farm house could be heated on anything less, but I am willing to consider it.
I have the 3 things DBoon is talking about - cast iron rads with TRV's and an Alpha pump. I Charge my tanks as described above and draw directly from the top of the tanks.
I already have a mixing valve sitting here so thought I might as well give it a try. I just have one concern. If I put the mixing valve before the Alpha so that the Alpha pulls through the MV, does this affect the operation of the Alpha? I don't think so but thought I should ask. Thanks.

 

[JohnDolz]

OK. I have been following this thread and must admit John that I am guilty as you were of thinking that I need very hot water to heat my house. There is no way that my drafty late 1800's farm house could be heated on anything less, but I am willing to consider it.
I have the 3 things DBoon is talking about - cast iron rads with TRV's and an Alpha pump. I Charge my tanks as described above and draw directly from the top of the tanks.
I already have a mixing valve sitting here so thought I might as well give it a try. I just have one concern. If I put the mixing valve before the Alpha so that the Alpha pulls through the MV, does this affect the operation of the Alpha? I don't think so but thought I should ask. Thanks.

Nice I look forward to reading about your results. I can't imagine it will impact your alpha pump but will leave it to others to comment. I'm assuming you are testing with a manual mixing valve (vs something tied to a controller and ODR) so keep in mind that the Design temp changes as outside temp changes. You will also need to find what temp works for your house. Tonight for example, it is -6C out and the Design temp for me is 43C, keeps me at about 22C. When you test this I suggest you try maintaining a temp vs. heating up to certain temp, as mentioned recovery is a bear at low temps.

 

[cpeltier]

Since you get me thinking and since I am leaving for the week I thought I would test my backup system. I find that even with it being reasonably cold today and windy I think I may have a challenge with short cycle (not sure what a good time between cycles really is, any idea?). The design temp is 114 today, when I run my thermal storage system my design and return temps are almost identical. I turned of the thermal to test the propane and of course the firing shut down almost instant (CH Demand temp met). Since I programmed the minimum time between firing to 5 minutes my circulators ran for a while dropping the return temp. Next time my boiler fired it fired for at least a few minutes before the return temp climbed enough that CH Demand Temp was met. I have a Modine Hydronic heater that is running in the basement, I know that returns really cold water - point is that if I had that shut off (which I prefer due to the noise) I would bet my return temps would return to supply temp very quickly. Wondering how you get around this? Maybe the answer is just knowing what an acceptable # of cycles per day is. I am going to let this run for an hour or wo and see if I maintain hose temps or not. Any insight is appreciated!

I did engineer my radiant loops carefully and I'm getting at least a ten degree delta across them. I even using a fixed speed pump (was a delta T pump now optioned for fixed speed because it never worked right and if you engineer it right you don't need a delta T mode). The flow rate on the smaller zones can get high since I'm using a single pump with zone valves and I have plans on replacing that with an Alpha in delta P mode to keep the delta T dead on across all loops all the time.

To answer your question generally I have a healthy 10 degree difference between supply and return although the flow rates can be quite variable - anywhere from 1.5 GPM to 11 GPM. Looking at the math on this I would expect my small zones to short cycle the LP boiler if run by themselves. My system does synchronize their operation with other zones so as to provide enough of a load (but not too much for the heat pump) to operate.

 

[cpeltier]

OK. I have been following this thread and must admit John that I am guilty as you were of thinking that I need very hot water to heat my house. There is no way that my drafty late 1800's farm house could be heated on anything less, but I am willing to consider it.
I have the 3 things DBoon is talking about - cast iron rads with TRV's and an Alpha pump. I Charge my tanks as described above and draw directly from the top of the tanks.
I already have a mixing valve sitting here so thought I might as well give it a try. I just have one concern. If I put the mixing valve before the Alpha so that the Alpha pulls through the MV, does this affect the operation of the Alpha? I don't think so but thought I should ask. Thanks.

It probably would be ok but it's always better to push through a pressure drop or restriction and pump away from your expansion tank which is the most important rule!

 

[Kristen]

There are no thermostats, just OneWire sensors embedded in the drywall in each zone

I would love to do that ... just have 1-wire temperature sensors in the rooms - both for historical data logging and something else to then control the valves etc. Everything I see has either thermostats or temperature sensors that are, to my thinking, "expensive".

I have used some 1-wire temperature sensors in the past, for a monitoring project, and I had to make up small circuit boards for each sensor (can;t even remember what components were needed now - but it wasn't much).

Did you have to do similar? or were you able to just wire the 1-wire sensors direct back to the control unit, and handle the requirements there?

 

[cpeltier]

I would love to do that ... just have 1-wire temperature sensors in the rooms - both for historical data logging and something else to then control the valves etc. Everything I see has either thermostats or temperature sensors that are, to my thinking, "expensive".

I have used some 1-wire temperature sensors in the past, for a monitoring project, and I had to make up small circuit boards for each sensor (can;t even remember what components were needed now - but it wasn't much).

Did you have to do similar? or were you able to just wire the 1-wire sensors direct back to the control unit, and handle the requirements there?

For that project (Vermont ski house) I used this on a Linux based system (TS-7800):
http://www.ibuttonlink.com/products/linkusbi
I also used a DS2409 based 1 wire hub that connected to above so that I could run twisted pair in different directions (Star topology) to daisy chain sensors.

My latest project (Home in PA) uses Modbus based OneWire controllers on the EasyIO which make it really simple. Examples of this are:
https://www.embeddedarm.com/products/board-detail.php?product=TS-1700
http://www.barix.com/products/barionet-family/barix/Product/show/barix-x8/ (about $70)

You can't daisy chain with these. Home runs per sensor but then you don't have to worry about knowing the address of the sensor either.

Modbus is great but it does require a controller with a Modbus master or a USB based interface for a PC or Linux based SBC.

 

[JohnDolz]

I did engineer my radiant loops carefully and I'm getting at least a ten degree delta across them. I even using a fixed speed pump (was a delta T pump now optioned for fixed speed because it never worked right and if you engineer it right you don't need a delta T mode). The flow rate on the smaller zones can get high since I'm using a single pump with zone valves and I have plans on replacing that with an Alpha in delta P mode to keep the delta T dead on across all loops all the time.

To answer your question generally I have a healthy 10 degree difference between supply and return although the flow rates can be quite variable - anywhere from 1.5 GPM to 11 GPM. Looking at the math on this I would expect my small zones to short cycle the LP boiler if run by themselves. My system does synchronize their operation with other zones so as to provide enough of a load (but not too much for the heat pump) to operate.

Thanks for the info. I have all my pumps set to their lowest speeds and have almost constant call from all zones (except my Modine Heater - I keep that zone a bit lower as it is the basement and I prefer not to hear the noise). I have an email out to Triangle Tube to get an understanding of what ideal firing length and time between firings. For now I am controlling it with the "minimum time between firings", currently set at 5 minutes per their previous recommendation. That recommendation was made to see what we got so I'm curious to hear back. At some point I may look at the overall engineering but since I rarely ever use it it doesn't make much sense unless it improves what I have doing with the wood boiler.

 

[Boardroom]

It probably would be ok but it's always better to push through a pressure drop or restriction and pump away from your expansion tank which is the most important rule!

My concern with putting the Alpha in front of the MV or restriction is that the Alpha would not feel a pressure drop from the load and would not know when to pump. If I put it after the MV it will feel the loss in pressure when a TRV opens. Sound right?

 

[cpeltier]

Is it a three port mixing valve? Your correct that pumping away would be correct. If it's a single pipe loop with TRVs on mono-flow Ts I don't think delta P mode would do much since the system head barely changes. If it's a two pipe setup then it may work better.

 

[JohnDolz]

Is it a three port mixing valve? Your correct that pumping away would be correct. If it's a single pipe loop with TRVs on mono-flow Ts I don't think delta P mode would do much since the system head barely changes. If it's a two pipe setup then it may work better.

As you can tell I have no engineering knowledge (or knowledge of he alpha). I can only share that it was recommended that the pump be nfront (or after) the mixing valve so that it is pulling the water through vs. pushing. I understand your discussion is at a much more sophisticated level so I will observe, see what I learn and see if I end up replumbing my whole house.