Matt Meier
New Member
I need to replace my boiler. The old one has gradually decayed over the past few years, and I've replaced small things here and there to keep it running. Last spring the boiler broke right as the weather broke, so we got lucky. The thermostatic shutoff broke, which subsequently blew off the pressure relief valve, which flooded the bottom, etc. There was enough of a mess, and it's old enough, that I think it's time for an upgrade. I've already checked with the city and the county, and they'll allow me to do the work. So, now I have to figure out what's best, and that's why I'm here.
My old system is a two-pipe forced hot water boiler, driven by two pumps. It was converted from steam a long time ago. The house is approximately 4600 square feet. It's a brick house that was built in stages, starting in the 1860s. I live in central Michigan, so it gets cold here. I've done a fair amount of research, and I have a reasonable heat-loss estimate (but I'm going to re-do it to verify), and I've measured all the radiators and that stuff. This whole thing fascinates me; I'm an engineer and about half of my work is related to controls. So I have a grand plan, which has also (miraculously) been cleared by the city.
Here's my basic plan:
1. Replace the boiler.
2. Re-route the pipes.
3. Install an array of electric valves OR small pumps to split the house from two zones into many zones
4. Install a master control circuit board (I've designed one; I just need to finalize a few things before I have it built) to run the pumps and interface between the thermostats and the boiler.
5. Install a remote wireless thermostat (also my own design) in each zone, and link them all to the master control board over a wireless network.
Short-term, I have a program written that will link up to the board from my computer, so I can re-program the timers and temperatures from my couch. Long-term, I'm going to write an interface for remote control, so I can access the house and re-program the system over the internet.
We only heat a small part of our house at any given time. At present, we have two large pumps, and we're lucky that they coincidentally split according to which rooms we use the most often. As a result, I know our boiler isn't running anywhere close to capacity. In fact, I've estimated that we only use about 60kBTU/h when we're there, but our heat-loss results in about 200kBTU/h. So, if I were to install a large condensing boiler, I'm pretty sure it would short-cycle. I've read about modulating systems, and two-stage systems (and three-stage, for that matter). I've also considered splitting the house, and installing two smaller boilers. Given our energy use, coupled with the cost of condensing boilers, I don't see the payoff happening within 20 years. So, I've been looking at traditional cast-iron units. Would it be wise to split them?
Also, if I were to install a single unit, why couldn't I keep them from short-cycling with intelligent controls? In other words, I know the temperature of the system, and I know that the thermostat just kicked in. Given that I'm detaching the pump controls from the boiler itself, if the water is already hot then why couldn't I just flip on the pump, and not send the signal to the boiler to turn on the burner? And why don't all boilers automatically all do that? I understand that some of the really fancy ones do, but it's an easy bit of logic that seems like it would provide significant gains for the homeowner. Old ones don't because the controls are nothing more than a couple relays and a valve, but they all have circuit boards now, don't they?
*Edited because I hit the 'submit' instead of 'preview' button.*
Thanks in advance for any input.
Matt
My old system is a two-pipe forced hot water boiler, driven by two pumps. It was converted from steam a long time ago. The house is approximately 4600 square feet. It's a brick house that was built in stages, starting in the 1860s. I live in central Michigan, so it gets cold here. I've done a fair amount of research, and I have a reasonable heat-loss estimate (but I'm going to re-do it to verify), and I've measured all the radiators and that stuff. This whole thing fascinates me; I'm an engineer and about half of my work is related to controls. So I have a grand plan, which has also (miraculously) been cleared by the city.
Here's my basic plan:
1. Replace the boiler.
2. Re-route the pipes.
3. Install an array of electric valves OR small pumps to split the house from two zones into many zones
4. Install a master control circuit board (I've designed one; I just need to finalize a few things before I have it built) to run the pumps and interface between the thermostats and the boiler.
5. Install a remote wireless thermostat (also my own design) in each zone, and link them all to the master control board over a wireless network.
Short-term, I have a program written that will link up to the board from my computer, so I can re-program the timers and temperatures from my couch. Long-term, I'm going to write an interface for remote control, so I can access the house and re-program the system over the internet.
We only heat a small part of our house at any given time. At present, we have two large pumps, and we're lucky that they coincidentally split according to which rooms we use the most often. As a result, I know our boiler isn't running anywhere close to capacity. In fact, I've estimated that we only use about 60kBTU/h when we're there, but our heat-loss results in about 200kBTU/h. So, if I were to install a large condensing boiler, I'm pretty sure it would short-cycle. I've read about modulating systems, and two-stage systems (and three-stage, for that matter). I've also considered splitting the house, and installing two smaller boilers. Given our energy use, coupled with the cost of condensing boilers, I don't see the payoff happening within 20 years. So, I've been looking at traditional cast-iron units. Would it be wise to split them?
Also, if I were to install a single unit, why couldn't I keep them from short-cycling with intelligent controls? In other words, I know the temperature of the system, and I know that the thermostat just kicked in. Given that I'm detaching the pump controls from the boiler itself, if the water is already hot then why couldn't I just flip on the pump, and not send the signal to the boiler to turn on the burner? And why don't all boilers automatically all do that? I understand that some of the really fancy ones do, but it's an easy bit of logic that seems like it would provide significant gains for the homeowner. Old ones don't because the controls are nothing more than a couple relays and a valve, but they all have circuit boards now, don't they?
*Edited because I hit the 'submit' instead of 'preview' button.*
Thanks in advance for any input.
Matt