Upgrade to 30 year old Radiant Heating System

plans_process

We would appreciate a sanity check. Our original radiant floor heating system was installed by us in 1994. 30 years later we need to replace the Polaris Water Heater (yes, the original but with a few parts replaced) and want to upgrade the system (The original system is a closed loop heat exchanger with one pump running the primary side and one pump running the secondary side) to a combi boiler and a circulator for each zone. We have attached a drawing () of what we think we want to do and would appreciate any feedback about the components and layout. (The actual physical layout is yet to be determined.)

The original system has two zones with three loops per zone. The tubing is RED Plasco Oxyguard 1/2 (CTS) PB2110 Potable. The system has been running with a glycol mix. Each of the upstairs Zone 1 loops are 165 +/- 4 feet and encased in 2 inch concrete (not gypcrete). Each of the downstairs Zone 2 loops are 264 +/-4 feet and encased in 4 inch concrete (slab on grade). The square foot area covered by Zone 1 and Zone 2 are approximately the same. Zone 2 loops are more closely spaced than Zone 1. The manifolds are 1 inch copper with ½ inch connectors to loops. All pipes and fittings are copper and brass.

The major components of the proposed system include: 1) Navien NFCH 175, 2) Caleffi SEP4, 3) Expansion tank (TBD), 4) Neutralizer (TBD), 5) Circulators (Grundfos UPSe 15-58??), and 6) Auto Fill Valve. (We are sussing out the code requirements for testable backflow preventers.)

We have discussed changing the manifolds (not sleek looking but still functional) but are uncertain if that would add any value or perhaps create problems with reconnecting to the Red Plasco Oxyguard. Also, we are wondering if we should continue to run a glycol mix or just water. If we run just water, what is recommended to flush out the loops to clear out the glycol?

The original installation 30 years ago was an adventure (laying out tubing in a snowstorm and determining if a contractor who put a wall in the wrong place had compromised it). We would not like to repeat any of the momentary heart failures, so feedback, comments, and suggestions would be most appreciated.

EdTheHeaterMan

This looks good, although your ability to draw like a draftsman is interesting. Very detailed. Nicely done.

@hot_rod Bob is the resident expert herein. I am guessing that the PEX is an oxygen barrier tubing by the name of it. and the existing manifolds should be just fine.

I believe that you can use tap water to flush out the glycol. You should discard it properly to a recycle location for antifreeze if it is not biodegradable. After getting mostly water thru the piping and the tubing, you may need to have the water tested to know if you need additional chemistry for the boiler. Bob has all that info.

hot_rod

No need for all those small air vents you have good purge points, the Sep 4 will finish off any air removal after the purge.

One purge valve on the bottom left Sep connection is really all you need. Purge one circuit at a time using the pump isolation valves. Really no need for iso valves on all the returns either. Unless you want to completely isolate a zone?

The Polaris was probably a 50 gallon tank? So it had a nice buffer component. The new boiler without that tank capacity will probably cycle a bit more. How does the heat load of the smallest zone match the lowest turndown of the boiler? That is a good way to see if a buffer tank may be a better option.

Do you really need glycol? Less $$ and maintenance hassle without it.

If it is PG glycol you could dilute it and flush it away. Or most oil change shops will take it, same with auto parts supply shops, NAPA, o-Reilly, Auto Zone, etc

plans_process

The Polaris is 34 gallons. The house is "wrapped" in R28 insulation, Structural InsulatedPanels. The Upper and Lower levels have almost equal square footage; however, the Upper Level/Zone 1 has more volume, surface area, and windows than the Lower Level/Zone 2. The Upper Level also has more passive solar gain and heat is augmented by a wood stove.

The Navien NFC 175 H heating capacity is per Navien documentation:

Heating Input
Min 13,3000 BTU/h
Max 175,000 BTU/h
Heating Capacity 161,000 BTU/h
TDR
DHW 15:1
Heating 13:1

Heat Loads: (approximate numbers)
Upper Level - Zone 1 - Total Loop Length 500 feet - Heat Load 9000 BTU/h
Lower Level - Zone 2 - Total Loop Length 800 feet - Heat Load 6000 BTU/h
Total House - Zone 1 & 2 - 15,000 BTU/h

Our heat demand is greater for DHW than heating. We are on the lower edges of the heating TDR and Min BTU/h.

hot_rod

So your smallest zone at design day is 6,000 BTU/hr. The lowest turndown is 13,3000 btu/hr. on that Navian

I love me a combi, but a 80- 100,000 btu/hr mod con boiler and indirect would be a better option.

Low turn down of 8,500 btu/hr , paired with a 60 or so gallon indirect would give you plenty DHW. Unless you have an unusually large DHW load?

Or a 10 gallon buffer added to that NFC 175 would get you a 15 minute run time with a 6,000 btu/hr load and a 13,3000 turndown.

plans_process

We have gone back to the proverbial and literal drawing board (Updated drawing attached) and read Idronics #17. (Still on a learning curve.)



We decided to use the buffer tank rather than the indirect because:
1. Space is limited - the buffer tank (Found a 12 gallon Ariston Water Heater with Multiple Ports and is 23" tall and 16" in diameter) is smaller, and
2. Our DHW gets concentrated use (simultaneous demands) at certain times.

Now the hard part - corresponding what we think we understand and the Navien NFC 175 settings. In the Navien settings (Our questions and concerns are in italics.)

1. Enable the Outdoor Temperature Reset (From the Navien NFC-H installation Manual) and the Preset for the Heat Load, High Mass Radiant

a. Heat Load: High Mass Radiant
i. Supply Set Point Range: 80-120°F
ii. Return Set Point Range: 70-101°F

b. Set Outdoor Temperature Range:
i. Set Outdoor Low Temperature at 14°F (Range Tlsp: -4°F to (Thsp - 9°F )) Note: The lowest temp in 202 was 17°F.
ii. Set Outdoor High Temperature Range at 70°F (Thsp: (Tlsp - 9°F ) to 104°F)


Navien Installation Manual NFC-H Condensing Combi-Boilers p. 140

2. Space Heating Operation Settings: With Temperature Sensor in top of Buffer Tank and connected as the System Supply Temperature Input:

a. Set Space Heat (SH) Set Temp at 120°F (Range: 104°F to 180°F):
i. Is this the temperature coming out of the boiler and would be the hottest water in the buffer tank?
ii. Per the Preset Heat Load, at 14 F, the Tlsp, the Supply Temperature would be 113 F.
iii. We have concerns about the tubing, RED Plasco Oxyguard 1/2 (CTS) PB2110, max operating temperature. Cannot find specification. Original system ran between 120 - 140 F; however, the supply went through heat exchanger and pipes (heat loss) before reaching the zone manifolds.

b. There is available a **Boost Interval Time: (Range 0-120 Minutes) See following explanation from Navien Manual.
i. " ** The boost interval time may be set to prevent interruption in space heating while using the Outdoor Reset Control mode, due to changes in heat load conditions. With the boost interval time enabled, the boiler increases the space heating supply temperature by 9°F (5°C) and the return temperature by 5°F (3°C) after a set time elapses. Once the boost interval time expires or the heat load demand is satisfied, the boiler will then revert back to its normal space heating settings." Navien Installation Manual NFC-H Condensing Combi-Boilers p. 113
ii. Is this necessary? It seems that the buffer tank will "prevent interruption in space heating".

c. Enable SH Control Method: 3 - System Supply Temperature in the buffer tank will trigger the boiler per the Preset Heat Load, High Mass Radiant.
d. Set SH Burner Off Differential at 2°F (Setting range: - 2°F (1°C) – 54°F (30°C))
i. Is it correct to use the smallest differential for high mass radiant? The high mass radiant heating system seems like a large ocean vessel whose response time to change course requires action, time, and then it responds.
e. Set SH Burner On Differential at 3°F: (Setting range: - 2°F (1°C) – 54°F (30°C))

A "small?" concern:

3. Is there any reason to think that the floor surface Temperature will go above 89°F? We haven't had this issue in the original system, but we were the human "thermostats" that turned the system on and off.

hot_rod

The sensor in iron the top 1/3 of the tank. The tank temperature will be maintained by the ODR requirement.

The highest temperature the tank should ever run at is whatever temperature you need at design day, if you have that number from a design?

I would guess the tube is rated for 180f, 100 psi. That is a typical rating for Pex tube. It should be stamped on the tube every 3’?

When you pipe a buffer like that, there are times when all flow goes from the boiler to the loads, as such the boost function could help come out of a deep set back, or a rapid drop in temperature driving the load up. You may not ever need it, it will only engage when the system tells it to.

Ideally a perfectly tuned ODR could give you nearly constant circulation The temperature adjusts to the ever-changing load of the spaces.

The surface temperature will depend on the r valve of the flooring, and the load of the space. You really should not run above 82f or so in a well designed system. That is a comfortable temperatur3 for bare feet. Some days it may be 78f, it depends on the load at any time.

It will take some fiddling to get this dialed in to your needs and lifestyle, there is no exact control logic that is perfect for everyone. That is why those boiler controls have so much adjustability