A tekmar 261 which is a 2 stage boiler control

Combined with disabling any thermostat/outdoor reset logic in the WtW unit and something to completely turn off the WtW when output temps are so high that just the gas boiler would be more efficient, that makes sense.

Posted By jonr on 15 Apr 2013 09:43 AM

A tekmar 261 which is a 2 stage boiler control

Combined with disabling any thermostat/outdoor reset logic in the WtW unit and something to completely turn off the WtW when output temps are so high that just the gas boiler would be more efficient, that makes sense.

A boiler control and a couple relays...For the purpose of comfort with the radiant, I guess running the Boiler as second stage and turning the high temp off at a certain outside temperature sounds reasonable, similar to an air sourced and a dual fuel setup. The split would disabled in the winter, and only come on for summer A/C.
I am still not warm with the 3 circulation pumps in series. 1 on the high temp and 2 on the split makes more sense.

Posted By docjenser on 15 Apr 2013 11:25 AM

Posted By jonr on 15 Apr 2013 09:43 AM

A tekmar 261 which is a 2 stage boiler control

Combined with disabling any thermostat/outdoor reset logic in the WtW unit and something to completely turn off the WtW when output temps are so high that just the gas boiler would be more efficient, that makes sense.

A boiler control and a couple relays...For the purpose of comfort with the radiant, I guess running the Boiler as second stage and turning the high temp off at a certain outside temperature sounds reasonable, similar to an air sourced and a dual fuel setup. The split would disabled in the winter, and only come on for summer A/C.
I am still not warm with the 3 circulation pumps in series. 1 on the high temp and 2 on the split makes more sense.

I'm trying to follow, and hope I'm doing okay.

If I understand, this scenario would require:
The addition of a buffer tank between the W2W and the Phoenix
Two new thermostats (the tekmar 261 for hydronic and a second stat for the split)
A new radiator in our kitchen.

The loop and piping are okay, and all equipment sizes are adequate.

"Throw out all 3 circulation pumps, and replace it with 1 Wilo Stratos pump, using a fraction of the power." Is this still a possible option? I am not savvy enough to know if this suggestion can stand alone or has to be paired with the other recommendations. By the way, our stat is a Honeywell THX9321. Will it control the hydronic in the way you described above?

The addition of a buffer tank between the W2W and the Phoenix

No, not needed. See http://welserver.com/WEL0267/ where a single tank is used on the space heating side (integration of the tank with one of the heaters makes no difference under steady state conditions).

You can split up the pumps so you can salvage what you have. One is serving the high temp and comes on when that is running, the other 2 would serve the split. Technically you only need a buffer tank of you have more than 1 zone for the radiant. Do you? Or is all in one radiant system, without different zones? However, the controlling now becomes more difficult. Thus I still suggest you use a buffer tank. Both should inject heat into the tank in parallel, first the high temp, then the boiler as second stage. The tekmar 261 would monitor the outside temp and fires the stages, depending on how much heat is needed.


You can then have a boiler control on the buffer tank and shut off the 1st stage when temps get too high for it to run efficient. The split would only be for a/c.

Again, here is an example:

http://welserver.com/WEL0545/


Loopfield is OK as long as both heat pump come on together. Your Thermostat is very advanced (Honeywell prestige), not sure what it is good for in your scenario.

Posted By jonr on 15 Apr 2013 02:10 PM

The addition of a buffer tank between the W2W and the Phoenix

No, not needed. See http://welserver.com/WEL0267/ where a single tank is used on the space heating side (integration of the tank with one of the heaters makes no difference under steady state conditions).

Do you have many installs like that jonr?

you only need a buffer tank of you have more than 1 zone for the radiant

Doc gets it right here - with only one zone (or all of your zones have sufficient flow to move the full output of the heat source(s) for some reasonable period), then you don't need any buffer tank at all (let alone two (the Phoenix counts as one)).

I find it interesting that just about all buffer tank plumbing designs cause some mixing of the radiator inlet water and the outlet water. Heat pumps are most efficient using the coolest (ie, the returning inlet) water available, not some mix. The fix isn't hard...

http://welserver.com/WEL0545/

This example seems pretty straight forward--even I can follow it. I think I understand why the original design had 2 stats, and I wish someone had just said the install required it, rather than trying to talk up the benefits of being able to carry the second stat from room to room.

Yes, we have one zone for our radiators. So it sounds like the ideal configuration would have a buffer tank.

Doc, do you mean in your last post that the loopfield is okay as long as both hp don't come on together?

Adding a buffer will allow both the gas boiler and the high temp geo to run simultaneously up until when the buffer gets too hot for the geo to be efficient. I'm guessing you would run all geo up to about 120 deg F, then supliment with gas till 130, then all gas past this point. Those points can be adjusted during the first winter testing. COP testing will show when its best to shift.

If you don't add the buffer, you can not run both at the same time and the logic can be set to just use the gas past a certain temp. I would think the cross over point would be somewhere around when the buffer needs to be around 120 - 130 def F when you should run just the gas. I am not sure where the geo efficiency drops so much that the gas becomes more cost effective.

Adding the buffer gives more system flexibilty. Using no buffer, you loose the abilty to run both at the same time, but it should give a cooler return temp that will improve geo efficiency some. Maybe a toss up, but I like the buffer.

If you don't add the buffer, you can not run both at the same time

Why do you think they can't run at the same time?

Hmm? I assumed the BTU output of the gas boiler at low fire would shoot the house loop up too fast without the buffer. Maybe a bad assumption on my part.

Posted By docjenser on 15 Apr 2013 03:55 AM

Posted By tamar on 15 Apr 2013 01:33 AM
Doc, I wish you were in Rochester/Buffalo, MN instead of Rochester/Buffalo, NY! I am wondering how our well-known installer gets away with not creating the type of schematics you and others have posted in this thread.

The schematics are not key, they just look pretty and are a bit PR. But they show us and others what design works well under certain conditions, and how well it works. We just take bit pride in making them look OK. As you discovered, the key is not only to make it work, but to make it work efficiently.
I really hate you to give up the radiant, since I am big fan of it. Find out what your installer is willing to do. We can help him to salvage the situation if he is willing to listen.

I will approach the installer with this info and figure out what he is willing to do. Thank so much for all the advice!!

Yes, gas is dirt cheap now, but once they start exporting it, it's going to go back up, just a question of how much and how soon, so I'd hesitate to give up the hydronic just yet. 

Maybe you don't want to, but here's a possible way you could get the hydronic unit working satisfactorily without a lot of major alterations. Set the circulator pump (the newer ones use less than 1 amp) to run continuously and just set the hydronic unit to maintain a steady temperature in the buffer tank and the radiators that is significantly lower than what would be required to maintain 68ºF house temperature at a given outdoor temperature. That can be done just by setting the parameters in the unit's internal software. Just as a guess, you could have it come on at say 45ºF outdoor temperature with a target water temperature of 90F, just barely warm, and set it to max out at say 115ºF when the outdoor temp is say 10ºF.   At those temperatures, it's always going to be running at a fairly high COP.  It won't ever overheat the house because it would never put out enough Btus to do so (if it does, just drop the target water temps a bit).  The forced air system would regulate the temperature with the hydronic always giving a secondary assist. You might occasionally need to manually switch to the gas boiler on really cold days/nights, but that ought to be pretty rare.

Posted By FrankZ on 16 Apr 2013 03:45 PM

Yes, gas is dirt cheap now, but once they start exporting it, it's going to go back up, just a question of how much and how soon, so I'd hesitate to give up the hydronic just yet. 

Maybe you don't want to, but here's a possible way you could get the hydronic unit working satisfactorily without a lot of major alterations. Set the circulator pump (the newer ones use less than 1 amp) to run continuously and just set the hydronic unit to maintain a steady temperature in the buffer tank and the radiators that is significantly lower than what would be required to maintain 68ºF house temperature at a given outdoor temperature. That can be done just by setting the parameters in the unit's internal software. Just as a guess, you could have it come on at say 45ºF outdoor temperature with a target water temperature of 90F, just barely warm, and set it to max out at say 115ºF when the outdoor temp is say 10ºF.   At those temperatures, it's always going to be running at a fairly high COP.  It won't ever overheat the house because it would never put out enough Btus to do so (if it does, just drop the target water temps a bit).  The forced air system would regulate the temperature with the hydronic always giving a secondary assist. You might occasionally need to manually switch to the gas boiler on really cold days/nights, but that ought to be pretty rare.

Thanks Frank. We have nothing against hydronic except for if it costs too much as it was initially installed. We thought we were making a decision to lead with hydronic even though it would be "less of a savings" for us.  We would still be happy with that, but we spent wayyyyy too much money on the install to also pay more than our old gas boiler to heat our house. Sounds like your suggestion might be one way to get there. Hopefully the experts will weigh in on this suggestion, and I can discuss it as one of the options with the installer.

....and now I'm going to get in over my head by saying I think Frank's suggestion means we *should* have a buffer tank and the pipes inside should be replaced with larger ones. How'm I doing??

OK, since more people start to suggest that the 3 ton high temp and the 5 ton split can run together, please do the pressure drop calculations and tell me how to run 24 gpm through the loopfield!?!? Even if you take it down to 2.5 gpm/tom, that would be 20 gpm. How do you get the flow up to 20-24 gpm?



Frank, Minneapolis 97% design temp is -16F. How much manual switch over do you want to do? Your suggestion to set the buffer target temp to 115F at 10F outside, which means entering water temp to the heatpump would be 115F and leaving temp at about 123F, will not work well. Capacity will be around 25 KBTU/H, and with an old Victorian with a heatloss around 70 KBTU, the balance point will be 30F for the 3 ton high temp. In reality, it will never reach 115 F buffer tank at 32F outside temperature. You are lucky if you get it up to 105F, at which temp the BTU output of the radiators will equal the heatloss and the BTU output of the 3 ton w-w.



That is why it never made sense to use a high temp here, since it will never reach the higher temps due to the lack of capacity. Now you want the split to kick in as the second stage, no a bad idea, but unfortunately the loopfield and the pumps do not get you enough flow to support both pumps continuously at the same time. They realized that and now they are up to 3 pumps in series already.



The last thing you need is this going from bad to worse. WEL 267 (http://welserver.com/WEL0267/) is a good example. 108,000 BTU heatloss at 2F. Old 1927 tudor.
6 ton WF feeds the radiators, balance point is about 36F, buffertank is at about 100F then. Gas Boiler then kicks in as second stage, feeding more BTUs to the buffertank. HP turns off at 125F buffer tank to let the boiler run alone. 135F buffertank temp are necessary to heat the house at 2F.



Sounds like Tamar needs something similar. If you want to run the baseload of the house with radiators and the w-w, and then have the second stage to be the split, you can do this, but the pumping and loopfield needs to change.

OK, this will work borderline, but it will work. One of the pumps need to go on the 3 ton, the other 2 have to go on the 5 ton. They only turn on when the HPs are running. The 3 ton needs a balance valve with a CV of 2.5 to restrict the flow to the 3 ton to 8.2 gpm. Then the (2) other 26-99 at the 5 ton will be able to pump 11.3 gpm, which is borderline. The 1' pipe inside to the wall needs to be replaced by 1.25". Checkvalves are needed to prevent backflow through the circulation pumps. That way you could run both HP at the same time, meaning you can put the W-W at first stage on the radiators, and could have the split come on as second stage.



It is more a comfort point, if you want the radiant to heat your house at colder temps, or you want the forced air to come on.

Posted By docjenser on 17 Apr 2013 02:51 AM

Frank, Minneapolis 97% design temp is -16F. How much manual switch over do you want to do? Your suggestion to set the buffer target temp to 115F at 10F outside, which means entering water temp to the heatpump would be 115F and leaving temp at about 123F, will not work well. Capacity will be around 25 KBTU/H, and with an old Victorian with a heatloss around 70 KBTU, the balance point will be 30F for the 3 ton high temp. In reality, it will never reach 115 F buffer tank at 32F outside temperature. You are lucky if you get it up to 105F, at which temp the BTU output of the radiators will equal the heatloss and the BTU output of the 3 ton w-w.

ACCA Manual-J sez -11F, as the 99% outside design temp (and not -16F as a 97F outside design temp, thus). It's better number to use something in the -10F range or even -8F, as a 97% number, lest we oversize it even further.  

Whatever dataset places the 97th percentile outside design temp at -16F for Minneapolis may not be including the past 15 years(?).  The coldest temp logged in MN this winter was only -11F (19 January 2013), according to weatherspark.com data. The 2012 low point was -15F (20 January), in 2011 it was -15F on 21 January, in 2010 it got to -15F on the 2nd & -14F on the 9th of January, but you have to go back to 2009 to find a temp below -16F.  You have to go back the second & third weeks of January 2009 to find temps below -16F, which makes it a very unlikely number for a 97% design temp, or even a 99% design temp.

This feels like another  "...10% here, 10% there..." type of design load creep toward the high-side of reality, something to be jealously guarded against, since in this case it becomes  "... a half-ton here, half-ton there...", with a measurable effect on actual peak water temps & net efficiency.

Luckily, with outdoor reset, the water temp will be set according to demand created by the actual outdoor temp, not some forum value. The maximum system output is way over sized, but with the right controls to stage the 3 systems, that isn't an efficiency issue (well, not an energy cost issue, build and maintenance costs ARE excessive).