HVAC System

Discussion in 'Off-Topic' started by jpanhalt, Feb 25, 2015.

  1. jpanhalt

    Thread Starter AAC Fanatic!

    Jan 18, 2008
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    My new home is a log cabin built in 1993. I am the third owner. The heating system is hot water baseboard heat. It has an outside woodburner (currently disconnected) and had an inside woodburner, which a previous owner sold separately. The current system, is simply a propane fueled system with a circulator pump. Domestic hot water is obtained by a heat exchanger from the same furnace that provides heat.

    Needless to say, the system has a ratsnest of thermostat, 24VAC control wires. In some cases, two, 18-2 thermostat cables are used to carry one signal. The main relay (White-Rodgers 829A-832) is a DPST relay and has become erratic. So, in my opinion, it is time to fix it and remove some of the band-aides.

    I have a basic understanding of 24VAC control systems and am planning to substitute some SSR's for the sticking relays. The main problem area I am facing is where there is a thermostat on the boiler. I assume the regular thermostats demand heat (five zones) and that thermostat monitors water temperature at the boiler. It appears that it does not allow the circulator to turn on until a threshold temperature is reached.

    My question is simply whether anyone can provide a link to a description of such systems. Most of my controls are White-Rodgers or Honeywell.

    John
     
    Last edited: Feb 26, 2015
  2. killivolt

    Active Member

    Jan 10, 2010
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    In the title of the Thread is this a combination Heating and Air-conditioning system? I'm confused about the 18-2 which is usually heating only.

    kv
     
  3. jpanhalt

    Thread Starter AAC Fanatic!

    Jan 18, 2008
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    It is heating and hot water only. I used "HVAC" because that is the category under which I find parts.

    John
     
  4. killivolt

    Active Member

    Jan 10, 2010
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    [​IMG]

    I found this basic diagram. You probably have already seen this.

    kv
     
  5. jpanhalt

    Thread Starter AAC Fanatic!

    Jan 18, 2008
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    Thanks, KV.

    A good part of the system I basically understand. For example, the return line from each zone is controlled by a Honeywell motorized valve (V8043F1036). When a thermostat in a zone calls for heat, the valve opens and wiring from the valve to the DPST switching relay (White-Rodgers 829A-832 now obsolete) controls the furnace and circulator pump. The furnace and domestic hot water are like a separate subsystem and are interconnected so so there is a shut off if the water gets too hot and a turn on, if the water gets too cold. That part uses a Honeywell Aquastat.

    This part I don't understand:

    In addition, there are two, hydronic zone valves (White-Rodgers #1311-10x), which apparently have the same function as the 13A02 valve you show. One of them is in the supply line to household heat; the other is in the supply line to the domestic hot water heat exchanger. I don't fully understand why either valve is in the system, and in particular, I don't understand why a valve in the supply to household heat is needed, since each zone has its own valve on its return line. In reading the installation directions for the #1311 valves, it describes using one on each zone (e.g., my system could be described as just 2 zones with one zone having 5 sub-zones) and does not mention using additional valves. To add to my confusion, I have not seen the rotor indicator disk in the valve (red arrow in attached) change positions depending on whether any thermostat is calling for heat or not.

    upload_2015-2-26_13-28-57.png

    Right now, I am thinking that the W-R 1311 valves may be functioning to prioritize heating, that is, hot water vs. house. I am not sure which has the greater priority or which thermostat exactly controls the valves. My guess is that the Aquastat is doing that. There are still lots of wires to trace. I was hoping there was a hydronic systems for dummies reference that showed pictures of W-R and Honeywell controls and explained what happens when you do things like rotate that disk manually.

    John
     
  6. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    You have the plumbing, the pumps, the boiler, and the heat exchangers (radiators)

    You would need to trace the "circuit" per se, to follow the water from intake to return. Just like you would any electronic circuit.

    The relay and valve you have shown is open and closed based on the thermostat reading in the zone.

    Here is a simple diagram found on the web. You will note there are no valves indicated nor any controls.

    [​IMG]

    Of course a home would have more than one "zone"

    [​IMG]
     
    Last edited: Feb 26, 2015
  7. jpanhalt

    Thread Starter AAC Fanatic!

    Jan 18, 2008
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    I think I found the culprit. Now, I will mention one piece of information that was "unintentionally" left out. When I returned from Cleveland on Wednesday, the basement had a strong odor of gas. Our propane smells more like garlic than the smell I associate with natural gas. After doing some diagnostics, I tentatively concluded it was because the system was cycling too frequently. I talked with the propane supplier, and he agreed that could be a cause. I had recently had a leak check, after the propane tank went empty. That also gives the same symptoms of cycling, exhausting, and smell. The exhausting is what blows a little propane into the living space and is considered normal for my system. It is actually a useful sign that the propane tank is empty. (I am on a keep-full account, but for various reasons the propane company had underestimated my needs.)

    I had guessed that the motorized valve in series with the household valves was related to the problem, but not the cause. The two zone valves mentioned above (White-Rodgers #1311-10x) create two major zones and the domestic hot water (DHW) seems to have priority. The DHW was set fairly high by the previous owner. I had had the local heating dealer check out the system about 3 years ago. He found that the Aquastat was set too high in his opinion. He lowered that to about 160°F, but didn't touch the 30-gallon indirect-heated hot-water tank. He also lowered the high cut-off of the burner to 180°F. What was happening is the tank would call for heat. open its main zone and the boiler would start. It would then shut down when the limits were reached, but before the DHW valve closed to let the bulk of the hot water go to the house. The house thermostats would call for heat, but it all went to the DHW. The interaction of the two zones and relatively low limits led to rapid cycling, which was accentuated when the outside air was -10°F.

    The Weil-McLain manual for my furnace suggests setting the hi-temp furnace cutoff to 220°F with a maximum of 240°F (115°C). I was a little hesitant to go all out on the temp setting. What I did was adjust the DHW down a bit, increase the Aguastat to 172-175°F, and increase the boiler high-cut-off to 190 to 193°F. Now, the DHW valve shuts off, the house gets hot water (I hooked up some TC probes and can watch the return temp drop as the DHW valve closes), and cycling has decreased. Outside temp has risen to 17°F, so the real test of those adjustments will await a colder evening. Once I become comfortable with the high-temp cut-off setting for the boiler, I will be able to use the Aquastat to compensate, if needed, for outside air temperature. One of my old, round, mercury thermostats seems a bit erratic, so that is getting replaced. One added twist is that the system was setup for dual heat with an outside wood burner that feeds a heat exchanger to the household system. The wood burner is not connected and is empty, but the household loop to the heat exchanger is not isolated. In fact, the Aquastat is attached to the return line from that heat exchanger. When the system shuts down, the temperature in the return line drops fairly rapidly. I may fiddle with the high-low spread on the Aquastat a little to reduce cycling even more, if needed.

    One of the frustrations is that the manuals suggest setting the Aquastat at least 10°F greater than the DHW setting, but the temperature correlates for very high, high, med, and low settings on the DHW are not given.

    In brief, the DHW was set too high, the boiler high-temp cutoff was set too low, and the Aquastat needed to be set a little higher. So far, no more gas smell either.

    The pressure relief on my system is set at 30 psi. Any recommendations for what a typical, high-temp cutoff setting of the boiler should be would be appreciated. By typical, I mean for cold climates.

    John
     
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