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| Hydronic Heating System Bypass |
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| jpanhalt:
Every change has made a little improvement. Tomorrow's plan is to remove the big Armstrong pump, which feeds the whole house and DHW, and check it our. I didn't want to dig into that at 3:00 PM local. Replacing it with a new Taco will require actual plumbing changes. A good part of today was spent driving to Lowes and Menards and getting some anticipated parts -- about 3 hours. Replaced the pressure release valve on the boiler, which was leaking, and looked into the boiler. Seems fine. With the system cool and refilled, that pump heated very slowly. Maybe it is working just by convection. Will update. John |
| floobydust:
The boiler controller has an outdoor reset? Just got mine fixed, the thermistor was reading about 10-15C degrees warmer than it actually was outdoors. So the boiler water temp was cool and sometimes intermittently going in warm weather shutdown. Argued with a few HVAC contractors for two years. Turns out it was cracked cable with some water in it. It needed to be shielded twisted-pair but ground not connected to earth-ground but just to the (floating) Tekmar controller input. The guy put it in conduit and seems OK for now. I would make sure the boiler water temp is bang on because it can be a goose chase. |
| jpanhalt:
There is no outside temperature gauge or reset for the propane-fired boiler.* The circulator in the boiler runs and gets up to water temperature. That system gauge is mechanical and seems reasonably accurate. That is, at 180°F, I cannot keep a finger on it. Flow from the boiler goes directly to the system circulator (see diagram in first post). Both circulators always run simultaneously whenever a room thermostat or DHW call for heat. The only temperature control outside the boiler and room thermostats is called an "Aquastat." It is on the main return pipe and shuts down the boiler when a set temperature for the return is reached. Currently, that setting is 160°F. Return temperature remains well below that now. The problem is that heat from the boiler loop is not getting to the various zones in the house. The zone values, which are in the return lines, do seem to operate as expected. That is, when the thermostat for a valve is calling for heat, the temperature of the corresponding source pipe increases. Albeit with the current problem, it only gets a little warmer. John *The outside wood burner does have its own temp gauges, controls, and circulator, but that system is isolated and disconnected at present. |
| floobydust:
About the bypass on the boiler, it is a mysterious thing because you would think water would just not bother flowing through the boiler and just take the bypass route. On one boiler here there is instead a ball valve as the bypass and I played around with it. If you close the valve, more flow through the boiler, greater delta T in temperature but it cavitates when closed a fair bit. As if the boiler cannot take full flow. If you open the ball valve, the boiler short-cycles because temperature comes up fast, it has too much heat for the amount of flow. I was told a boiler has efficiency curves and a factory-recommended delta T across it and that determines the ball valve setting. For the same boiler with a double T-fitting (bypass) I asked how that works and was told the water density difference between boiler inlet and outlet due to the temperature difference is enough to make the denser cold water go into the boiler instead of bypassing it. There's some physics involved. Taco has proportional valves for the bypass I don't know much about them. Another troubleshooting technique is using a thermal imaging camera to see what is going on. It sounds like you have restricted flow from a lazy zone valve or too much plumbing and maybe a booster pump would help if the boiler is seeing too much outlet pressure impeding flow. You have to know the pump curves. A "bigger" pump may not do much better than a small pump if pressure difference (inlet and outlet) I think is big. A Bell & Gossett has a flat pump curve, meaning same medium flow rate regardless of delta P. I was thinking of your system acting like there is a kink in the garden hose. Bigger pump still can't do much. Sometimes these hydronic systems are poorly designed and never work that great from day #1. |
| mjs:
Check out the boiler circulator pump. The system functions likely like this (I know district heating systems better than propane..) - When the boiler is off, the circulation goes through the straight connection. Let's say this flow is 20 lpm. - When the boiler is on, its circulation pump causes part of the flow to go through boiler circuit instead of straight connection piece - The shunt valve in the boiler circuit (usually a three way mixing valve here) is used to limit/control the temperature going out from the boiler loop to distribution loop Since the heating loop circulation pump is 'sucking' from the straight connection, the flow coming from the boiler loop goes rather to the heating loop than back to boiler loop. The reason for having a separate flow in the heat delivery circuit is that the water mass also acts as a heating energy buffer. You can even use a buffer tank to increase the capacity and reduce the duty cycle of the heat source. |
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