Boiler Replacement Project (Success! and Thank You!!!)

[Matt Meier]

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

 

[Dana]

With the thermal mass of all that water in the fat piping of 2-pipe steam and high volume radiators you usually don't have to worry about short-cycling,

I'd be surprised if your true heat load for a 4600' house is 200,000 BTU/hr at the 99% outside design temp, even if it's only minimally insulated. But since you have a heating history there's a fairly straightforward way to figure that out. If you're gone a lot of the time with the thermostats set to something really low, you'll have to use a lower heating base temperature, maybe 5F above the temp you had the T-stats set to (eg. If you set 'em at 50F, use base 55F as the heating degree-day base), then use the BTU/degree-hour constant make a linear projection of what it would be at 70F indoors instead of 50F. Most completely uninsulated 4600' houses would still only come in at about 100-115,000 BTU/hr @ 0F (most of MI is in positive single-digits for a design temp) if it's been reasonably tightened up and at least has storm windows over the antique single-panes, and with some insulation could come in around 75-80,000 BTU/hr.

You may find this to be useful in your analysis too, and may tip the balance toward or away from condensing boilers.

The installed cost of condensing boilers can be even cheaper than mid-efficiency cast iron, due to the cost of the (absolutely necessary in your climate) flue liners that you would need with mid-efficiency cast iron. If you're micro-zoning it a lower cost right-sized fire-tube mod-con with a 10:1 turn down ratio (eg. HTP UFT series , but there are others) and a single (or two, in your scenario) ECM-drive pump with zone valves is usually the "right" thing to do, even with the higher mass radiation, if only because it's simple tweakable, and easy to implement. Fire-tube mod-cons have comparatively low pumping head, which makes them easy to design around, and can usually be drop-in replacements for cast-iron without needing primary/secondary plumbing to manage higher flows.

Most commercial zone controllers operate the pumps/zone valves independently of the boiler's burner, and only "enable" the boiler letting the boiler's internal controls manage the boiler temperature. When the boiler's high temp is reached the pumps keep going as long as the t-stats are still calling for heat, but the burner only re-fires when the low-limit is reached. Smarter boiler controls manage the temperature limits base on recent zone call history to purge the boiler of heat down to an even lower temperature before firing up. But with on/off single-firing rate boilers a single micro-zones calling for heat can cause excessive cycle if there isn't sufficient thermal mass in the boiler & zone plumbing & radiation. With modulating boilers it doesn't take nearly as much thermal mass to manage the cycling.

 

[Sponsor]

 

[Matt Meier]

Those are some great links. Are you the Dana that wrote them? If so, then good work. They're very clear and easy to follow.

I also thought that 200k seemed high, but I've gotten there through a couple methods. I did a loss estimate based on our history last winter, and it came out to be around 190kBTU/h. We were also "lucky" enough to have our control relay get stuck on a couple winters ago while we were in Pasadena. When we got home, the boiler had been running for probably a week, based on our bill. We have a 300kBTU/h gross system that reportedly (on the nameplate) puts out 240kBTU/h. The pumps were both running full-on, and the water hadn't reached the 185° shutoff point. The outdoor temperature was about 20°, and the house was a little over 80°. Our system is a little old, so it probably wasn't really putting out 240kBTU/h. We don't want our house to be 80° in the winter, so I dropped that down to 70°, bringing the design temperature down to 10° (a little high for our town, but close enough). All things considered, that puts us in about the right neighborhood for 200kBTU/h. I've had two heat-loss calculators put us between 180kBTU/h and 210kBTU/h. I'm not sure what to really think on this one, and I'm actually quite worried that I'm going to go overboard with the system size. I plan on taking some much more detailed estimates, and instead of the calculators I'm just going to do my own math for heat loss at various operating points.

My main concern is what basically amounts to two disparate demands. Sometimes we need a lot of heat, but most of the time we don't. A boiler that is capable of modulating down to 10% sounds like it would do the trick, but the price tag looks like it's significantly higher than a standard 85% unit, hence the original consideration of a two-unit system. I'm still waffling a little bit here. Are there any obvious disadvantages to a two-boiler setup, other than initial cost? Based on what I've found on the web, it would still be thousand(s) cheaper than a similarly-sized single mod-con.

One other thing I encountered in those articles was the danger of microzoning. With an intelligent, somewhat sentient system I should be able to avoid those issues, shouldn't I? What I mean is, if I know the demand cycles from the various zones, shouldn't I be able to force them to overlap? Of course, I can't continue to ignore a particular request forever, but if one zone is asking for heat then surely another isn't far behind. I could basically stack them until I got enough requests before sending them through to the boiler. We also have a large two-story stairwell/hallway with two radiators that I could use to suck up extra demand. In other words, if bedroom A is the only zone asking for heat, I could just fire up the hallway as an extra load, which would gradually diffuse its heat into the other rooms. Hopefully I'm not being myopic here.

I do plan on using a variable-speed pump. I've actually been told that I can run my current pumps at various speeds and they should work fine, but I'm not a fluids guy, so I don't know how pump design plays into this, so I'm going to do a little more research before committing to that.

I also should have added that I have a relatively new flue liner (probably 10-15 years old). I'm going to replace the water heater, too, so I'll naturally avoid having an atmospheric vent water heater if I put in a condensing boiler.

Thanks for the reply. Reading those links makes me feel a lot better about what I've come up with so far.

Matt

 

[Dana]

Using short-term behavior on the boiler's operation as a means of measuring the true heat load is fraught with error. Fuel use over a winter period of weeks or months is far more accurate.

Most online heat load calculators are pure junk, others hew pretty close to ACCA Manual-J methods, which is pretty good if you have the building construction materials & methods described well enough. A common large (to very-large) error in many calculations is the air infiltration & ventilation loads. The default settings on many load calculation tools are nearly insanely high. If you want to DIY it, you can use an I=B=R methodology, but you may have to calculate your own U-factors for non-standard construction. Most newbies (and many/most HVAC contractors) tend to use overly conservative assumptions about R-values/U-factors and air leakage, which incrementally increases the calculated load, which as a rule leads to significant oversizing. The better (and true to Manual-J) way to go is to be aggressive about assumptions, then upsize by no more than 1.4x at the end.

I'm still very skeptical of 200,000 BTU/hr of heat load at 0F (or 10F) of any 4600' house- that's a ratio of 43 BTU/hr per square foot of conditioned space. I've yet to see a mid-19th century antique that has had reasonable upgrades for insulation, glazing & air sealing come in at a ratio over 35-36 BTU/hr per square foot. Most come in under 30 BTU/hr-ft^2, even single-wythe brick + plaster.

Getting the size right is important for boiler efficiency, more so for cast iron than for modulating boilers. Oversizing cast iron boilers has a high standby loss adder, and increases the risks of excessive flue condensation for mid-efficiency boiler. An 85% boiler absolutely needs a correctly sized flue liner in your location, which adds to the installed cost. When looking at the total installed cost of the simpler fire-tube mod-cons compared to pretty-good 85% cast iron, it's pretty much a wash at best, and often more expensive to go with cast iron in a retrofit like this. The PVC vent piping of mod-cons is dirt cheap compared to lining a flue with B-vent or stainless flex.

HTP's UFT series is comparable to or cheaper than most 85% efficiency cast iron boilers. The Westinghouse-badged versions of that series are identical under the hood, and are sometimes even cheaper. Even the largest comes in under $3K . The HTP-badged versions are usually competitively priced as well. Pretty good 7-8 plate cast iron beasts with ~200K of output run in the $3-3.5K range, and have more expensive venting, higher local air pollution, do not modulate with load, and cost 15%+ more to operate per year (even more per year if it's oversized for your as-used load.)

Yes, it's possible to force micro-zones to overlap or heat purge into zones to limit the amount of burner cycling, and that's even easier to do when you have a significant amount of thermal mass in the radiation & distribution plumbing, but it's pretty kludgey compared to correctly sizing a mod-con, tweaking in the outdoor reset curve to get guaranteed overlap, and nearly continuous burns- a handful of off-cycles per day for most of the season.

If you're not yet clear on how to spec a pump, you need to get serious about taking the Jr. Hydronic Engineering class before diving into a micro-zoned system, independently of the boiler sizing issues. DIY hydronic design of more than the simplest of systems usually results in buying too much hardware up front, often of the wrong type, which then has to be replaced at considerable expense later. It's far better to hire a competent hydronic designer to spec every pump & valve in the system (even if you're insisting on your own customized system controller), which will usually save more in system cost than the cost of the design, even if all the plumbing is DIY. If installing the boiler yourself it pays to study up on the basics to avoid unnecessary capacity & efficiency robbing or pump-destroying installation errors- there's only so much you can fit into a system schematic & bill of materials, and there are dozens of ways of screwing it up even if you're starting with the right hardware.

And yes, I confess authorship of those bloggery bits I pointed you to.

 

[Matt Meier]

I'm not concerned about the pump/piping/valve sizing. I'm completely confident I can do all that; I've done a ton of reading. It's the pump itself that I haven't got the information on. What I mean is, I can run my pump motor at any speed I want. However, will it pump water appropriately? I know modern downhole well pumps can, but I don't know whether an old hydronic pump will work well at various speeds. Has the pump design itself changed significantly with the advent of variable-speed units? That's the question I'm working on. Where can I find the Jr. Hydronic Engineering class?

I think you've got me convinced that my heat loss is wrong, so I'm definitely going to go ahead with a full-on manual measurement. Here are some factors that seem to have tipped the scales for the worse: We don't have insulation, and the glazing is all original. We do have two-layer brick walls, and the tuckpointing is reasonable in most places. Some spots it's pretty holey. Our windows are enormous. We have two bay windows with over 100 square feet of glass, and another two with over 80ft². Most of the windows are floor-to-ceiling, so they have some pretty big surface area. Our ceilings are 10' in half the house; 9'/8' in the other half.

Still, I'm glad I was initially wary about the 200kBTU/h number.

Finally, does anyone have suggestions on where I should look to buy a boiler? It seems like my references, which were various websites that I've found through Google, are wildly expensive. That Westinghouse unit, assuming it's not oversized, is remarkably inexpensive compared to where I've been shopping. I'm on hold with HTP to see if I can find a distributor.

 

[Matt Meier]

Also, it wasn't entirely clear from my other post: I did two history loss estimates. One was the 190k from this past year (I took our heating degree-days from this year and converted to an average winter, because it was pretty warm), and the one-week fiasco was a completely separate year.

Matt

 

[Dana]

All original windows, but without any retrofit weatherstripping or storm windows?

No attic insulation, even?

If that is the case you really could be up there, but there is a ton of low hanging fruit on the retrofit weatherization front to be had, that will improve comfort & efficiency by quite a bit. Fixing all the big and obvious air leaks first would be a good start, followed by blower-door directed air sealing by some pros who specialize in that sort of thing would be well worth it prior to insulating any of it.

Low-E storm windows can turn antique wood sash windows into net energy gainers and cut the window air leakage (by a lot) and improve the U-factor of the window from about U1.0 to about U0.034 or so, reducing the heat load of the windows by about 2/3. They're more expensive than clear glass storms, but have a quicker pay back. They don't have to look like crap either- they even use them on historical buildings in my area.

John Seigethaler is a pretty good self-promoter of his own hydronic design publications and other materials, which would be a pretty good Jr Hydronic Engineering course if you really dove in. Most newbies using his materials tend to over design things a bit, and practical experience still counts.

 

[Matt Meier]

Alright. I'm better-equipped for this now. I did a complete manual estimate for my heat-loss. We have a few rooms that aren't heated One of them we used for canned goods, but we had to stop because the jars crack in the winter from the cold. It's separated from the house by a hollow-core interior door. I know. We're working on it. Anyway, I basically cut those rooms off from the heat-loss calculation.

Walls: R4, 3000ft² (not counting windows and doors). They are two layers of brick with a cavity in-between and 0.5" of plaster on the inside. I added the air film for the inside. We rarely have still air here, so I ignored the external air film.

Doors: R3, 160ft². This is a hard one, because the doors vary quite a bit. Some are updated, and some are original. Some have storm doors, and some don't. I added them all up, and the number I gave is the equivalent R-value for the total door surface area.

Windows: R2, 576ft². They're single-pane, but we do have storm windows (some of them are over 100 years old). Many of the storm windows are coming apart, and it's getting tough to find parts. Some windows have been caulked shut, which helps, but the glass is loose in most. I'm pretty sure none of them is holding R2 right now, but we're slowly rebuilding them and replacing the storm windows, so I figure if it's a little cold for a few years then we can hide under some blankets.

Ceiling/Attic: R22, 2200ft². Yes, there is some insulation there. We're going to bring it up to 5.5" all around in the near future. We can't go higher for the time being because we're not allowed to cover wiring that's tacked to the top of the joists. We'll move the wiring eventually and add more insulation, but I don't know when. I ignored the faster heat loss through the lumber, and just assumed it to be all insulation.

Basement: R1, 392ft². We have about two feet of exposed fieldstone foundation for most of the house. It's approximately a foot thick, as far as I can tell. It's not a huge area, and doubling the thickness isn't going to swing the issue here. I know both basements hold around 60° except for when it's really cold. One is a little warmer, but it's easier this way. We have windows, but they're boarded up, and some of them are covered by porches. I ignored them. I ignored heat loss to the soil as well.

I didn't figure in the floor, because that only loses heat to the basement, which subsequently loses heat to the outside, and we only care about heat exiting the house.

I set the design temperature to 2°. I found the 99% value for Lansing, the closest city. The temperature here is usually a bit colder than it is in Lansing, but close enough.

I set the internal temperature to 70° (except the 60° basement). While we don't keep the house that warm, we do warm things up a little when we have company over.

Ignoring air infiltration, that brings us to 140kBTU/h. If we add in air infiltration it will bump that number up, but not a ton; our house isn't drafty, and we're working on improving our windows and doors anyway. Multiplying by 1.4, we're in the 190s. I don't like that number, but given the additional detail, is it still completely bonkers? Where are my assumptions wrong?

In any case, after looking harder at pricing, I'm almost certainly going with a single mod-con boiler. Now I need to get the pipes out through a stone wall.

Matt

 

[Matt Meier]

I also found an error in my original heating history estimate. When I ran the heat calculation, I scaled the result too much. I had quickly assumed that I would need twice the heat to bring the rest of the house up to a comfortable temperature. However, that's obviously not true, because it was already at 55-60°. So, re-estimating with some more care, and adjusting with more detail for which parts of the house were which temperature, it looks like 140-150kBTU/h is what we would need to reach 70° on a 2° day.

I suppose that means my heat loss wasn't especially aggressive. Based on the assumptions, does that sound about right?

Again, thanks for the help. It's been invaluable so far.

Matt

 

[NY_Rob]

If you're settled on 140-150kBTU for heat-loss.... you need to look at number of zones, zone length, length of radiator per loop, etc... now.

The HTP UFT mod-cons are direct piped- you can use a Delta-P circulator like the Grundfos Alpha which makes zoning with zone valves much simpler as far as maintaining correct flow rate regardless of zones opening and closing. No need to re-invent the wheel with your own controls, pump logic, etc... the mod-con boiler manufacturer and "smart pump" manufacturer has already done that for you and the hardware is inexpensive now.

For T-Stats, if you want remote (via lan/wan/android/etc..) control capabilities... look into a Z-Wave system (self healing mesh net). I've had Z-wave T-stats for 5yrs now and they've been flawless. The heavily advertised Nest T-Stats are problematic and most heating pros hate them. The Z-wave T-stats are like regular modern programmable T-stats.. but they can communicate with the Z-Wave bridge device (which can also control/monitor your door locks, electrical outlets, etc..) for remote monitor & remote control.

One last note that I wasn't aware of when I first started my education into mod-con boilers... you pretty much abandon nite-time T-stat setback. The structure is kept pretty much at an even temp night & day all heating season long. The idea is to have the circulator running 20+ hrs per day with the boiler just meeting the current heat-loss via the outdoor reset sensor.

 

[Dana]

Unless you're having people over and socializing at 6AM on the coldest night of the year (when the 99% outside design temp actually occurs) there is no need to use anything but the code-min 68F for an indoor design temp. It's unlikely to make a difference in your boiler sizing, but it might.

A140-150K is still on the high side of average, but it could be real enough for the as-is-where-is condition of the house. But you should really be running the load numbers on the "after intended improvements" picture. If you do that you'll notice that a 1.4x oversizing factor of the new-improved number will still more than cover the 99% load of the house as it existed last year.

You can't really ignore the floor & basement losses. An unheated uninsulated basement can easilydrop below 50F during the cold snaps in your location which would be a 18-25F delta on a typically ~R2 (U0.5) floor in a 68F room. At a 20F delta you're looking at about 10 BTU/hr per square foot of heat load, and assuming you have something like 2300' of floor (assuming 4600' is 2 storys), that's 23,000 BTU/hr, a double-digit percentage of your total. If the basement is unfinished, not built out as living space it's still reasonable to insulate and air seal those walls from the interior, which drops the floor losses by an order of magnitude, and raises the barefoot comfort level. Depending on brick & mortar type you may want to apply a sacrificial parge of lime mortar over it before insulating. Check back here (or over on the GBA site) on how to insulate antique basements without going into the mold farming biz.

Since you're replacing storm windows it pays to look seriously at low-E glazing for the storms, which will bump performance into the R3 (U0.33) range. With 576' of R2 (U0.5) window and a 66F delta (68F-2F=66F) the window losses are running about 19,000 BTU/hr, but with low-E storms throughout that drops to 12-13,000 BTU/hr for a 6000 BTU/hr savings. That is also a bump in cool weather comfort you can actually feel, and reduces fuel use by even more than the heat load number imply, since the solar gain factor of hard coat low-E is still pretty high, and the windows all become net energy gainers- even those facing north! Harvey Tru-Channels are the most air-tight in the industry, and have a low-E glazing option, but they're pretty much a northeast regional player. The better grade Larson low-E storm windows (commonly sold through the blue & orange box store chains) are pretty good too, and well worth the upcharge over their lowest cost versions. More bedtime reading on the subject lives here.

Even at 1.2x oversizing you will still have very reasonable recovery ramp times when bringing up a less-used zone from 50F to 70F- no need for anything like 2x. ASHRAE recommends 1.4x oversizing as the best efficiency & comfort compromise for 1-speed on/off boilers, which guarantees you're covered at the 99.9th percentile bin, and has fairly expedient ramp times from setback. In your case you can probably do fine with zero oversizing, since most of the time you're not using a significant fraction of the house, and 99% of the time it's warmer than the 99th percentile temperature bin. Even on design day when temps drop that load, by the middle of the afternoon you would have 20% or more of margin on the afternoon's heat load with the boiler sized EXACTLY at the 99% load. Even undersizing slightly isn't a big deal, and can work.

Be aware that some jurisdictions (notably some counties in NY state, or maybe it's a state-wide thing) have a minimum oversizing factor greater than 1x and require a Manual-J from a certified professional. Check your the local codes before diving in if cutting it close to the margin.. But if a mod-con is 1.2x oversized for the load and the next size up is 1.7x oversized, you'll usually be better off with the smaller boiler, especially if you're micro-zoning.

 

[Matt Meier]

All the estimates were post-near-term-improvements, so I feel OK about those. If I drop to 68° and adjust the windows to R3, I cut about 10kBTU/h off. I didn't ignore the basement losses completely. Just the basement-to-soil losses. The basement was losing about 22,000BTU/h through the fieldstone to the outside air. I thought maybe that was high, but there are losses to the soil, so I figured they would balance.

At any rate, I feel much better having come in significantly lower than where I started. I'm going to go through all the data one more time to see whether I can convince myself to do something smaller. I've actually considered setting up a lumped-circuit thermal model, because let's be honest. This is a science project. Then I can watch how individual rooms will heat in a transient state, like when we get home with our friends after a football game, and realize we had forgotten to set their radiator to turn on...Oh, the possibilities!

Rob, I had originally looked into off-the-shelf remote systems, but their price was just way too high. The cheapest thermostat I could find with wireless connectivity of any sort was $75. I can build five of my own for that price, so I'm probably not going to change my mind on that one. Besides, it's more fun to set up my own, and then I can impress my friends.

The automated motor/drive has always intrigued me. I have to ask, though: Do the pressure-regulating ones modulate the pressure differential based on system load? In other words, suppose the boiler is running at 150° output temperature one day, and 120° a few weeks later. How does the pump know to adjust the pressure to guarantee that the radiators will see the proper flow? Or, am I wandering around in the realm of the theoretical, when in reality the difference doesn't matter, and we just make sure the reset curve on the boiler is set according to the fixed pressure differential?

The other turn-off with the production ECM pumps was the fact that "variable speed" pumps really are just a series of fixed operating points. With more than a couple zones coming in and out, I'm concerned the stepped speeds won't be able to adjust finely enough. Again, am I overthinking this one? I usually do, which is ironic considering I'm usually the "That? THAT isn't going to make a difference" guy.

Matt

 

[NY_Rob]

Hi Matt...
FWIW- I buy the Z-Wave T-stats from ebay- the CT30 is about $19 and the Z-Wave module for it is about $17 so you can put together a working Z-Wave T-stat for $36. Of course you still need the Z-Wave gateway device, but that's for another discussion. I respect your decision to "roll your own" wireless T-stats. I'm a big Raspberry Pi fan, I don't know if you've looked into that for home autonmation?

As to the Delta-P pumps, the Grundfos Alpha has three different modes of operation, take a look at the operation/performance page from the Alpha's manual for descriptions of the three modes:

 

[Dana]

ECM drive pumps come in many different flavors, and it doesn't take a lot of research to disabuse yourself of the notion that the speeds only come in discrete steps. The built-in controls come in a number of different modes, to control for things such as delta-T, pressure deltas, etc. The motor efficiencies are also significantly higher than any AC pumps, at any pumping rate or pumping head. Once you know your strategy and flow requirements, there are are several suitable options & approaches out there.

The heat losses to dry sandy soil are very small, due to the insulating characteristics of the soil itself, and doesn't change dramatically over the course of a year- a DC signal if you like, but a small one. Your deep subsoil temps central MI are ~45-47F, but it doesn't take much insulating value to the soil to limit the losses to even a 65F basement pretty small (and to a 50F basement it's miniscule.)

The fieldstone foundation is quite lossy above grade due to much lower R and much bigger peak delta-Ts, with the load varying with outdoor temp hourly, but with a time delay on the order of an hour or two. Below grade the daily variations are small, but have significant changes over the course of a winter. The design frost depth in most of MI is 40-45". Insulating a field stone foundation with ~2" of closed cell polyurethane (about $2-2.25 per square foot) is "worth it" on a fuel use basis, but also on a summertime mold-growth potential basis. With a ground vapor barrier on the floor and ~R10-R13 on the walls both ground moisture and humid summertime air infiltration are curtailed, and the average temp in the basement increases, which decreases the relative humidity. This reduces the amount of mechanical dehumidification needed to control "musty basement" smells and mold/mildew growth on susceptible items in the basement.

If it's a dirt floor, there is also a rationale for putting 1.5-2" of EPS foam board under the vapor barrier, and pouring a slab over it (even a 2" not structural rat-slab) to protect it. With sub-slab foam & vapor barrier the temperature of the slab temp will mostly track near or above the outdoor dew points in summer, making it possible to even stack cardboard boxes directly on the slab with minimal mold risk. The "payback" for 2" of EPS on the floor is small in terms of reduced energy use, but it makes the space more useful (and more pleasant to work in.) If there is a pre-existing slab (in most cases it's a 1-2" rat slab in antiques that old), laying foam & vapor barrier on the old slab with a new slab above it works. If the flood risk is near-zero you could even put down a wooden subfloor over the floor foam instead of concrete.

 

[Dana]

BTW: What are you currently doing for domestic hot water, and are you planning for the new boiler to serve that load?

 

[Matt Meier]

Thanks for the pump page. I had misinterpreted that; I thought the CP mode jumped from one speed to the next, but that's obviously not right.

Our basement is remarkably dry. I lazily leave boxes on the floor sometimes, but they're fine. I throw my rags and work clothes in a corner when I take them off, and wash them every few months. They never get damp. It's a miracle.

I'm not sure yet about the hot water. Again, we're an odd situation. We do occasionally shower (usually in the springtime), and I wash dishes by hand. Our washing machine is usually on cold because we're tall, and hot water makes our sleeves too short. Besides that, we don't use much hot water, except when we have company. Then we will run upwards of 10 consecutive people through our shower while simultaneously using the half-bath for primping and preening, while I wash tons of dishes. We have a badly oversized gas-fired heater, which doesn't regulate its temperature very well anymore, so it's time for a replacement. It's atmospherically-vented, so I'm going to have to replace it anyway. We're a good candidate for an on-demand unit. I haven't done my research yet on combination boilers, or on indirect tanks, but that's my next step after I estimate our individual room heat loss, get our radiators measured, and figure out how to split up the house.

I think that just leaves the question about how the pump "knows" to adjust the pressure differential based on the different heating demands, or whether that even matters. For example, let's assume (for now...actual sizing to come) that all our old steam radiators can successfully heat the house when the boiler pumps water at 140°F. As a hypothetical case, suppose one radiator circuit delivers 10kBTU/h with design temperature at 140°F hot water, 20° temperature drop, and 68°F in the room. Naturally, this won't be happening all the time, so when it's warmer outside, the boiler will drop its temperature down to something lower. Given the same pressure drop across the piping, we're going to see the same flow rate in the pipes. However, the heat emitted from the radiators will be lower (less temperature drop between the water and the room), so that particular flow will result in a lower temperature drop for the water, and we might be operating at, say, dT = 10° across the radiator.

My concern is: How does the pump know it should slow down the flow? Does that matter? As long as the boiler is seeing return water cool enough to condense, do we care? I know the pump is running harder than necessary, so it will be drawing more energy than necessary, but maybe that's insignificant. I'm intrigued by the "AUTOADAPT" function, but the explanation isn't much more than "Just trust us. It works awesome!"

My original plan to combat the issue was to use variable electric valves on each circuit instead of on/off zone valves, and the controller could adjust the dP on the pump and the valve position according to the temperature feedback from each loop. With some basic AI it could even learn to adjust the integrated system performance over time, and then fine-tune the system balance, so the rooms continue to heat evently. However, I'm not finding many options for (affordable) modulating valves. Again, this might be an example of overthinking it. Is it even worthwhile to try to maintain a particular dT?

Matt

 

[Dana]

An indirect fired HW heater running as a priority zone with 150-200K boiler driving it can deliver more than 3x as much hot water per hour as a typical 50-60 gallon standalone, an more than 2x that of the smallest commercial gas HW heaters, with much lower standby losses than any center-flue type gas HW heater. Even a 100K boiler with an indirect is enough to support a 24/365 shower. If you size the volume of the indirect tank for the largest tub you need to fill, the fill rate won't be constrained by the burner size. At your space heating load the boiler has enough burner that you'll NEVER run out of hot water doing consecutive showers, no matter how small the tank.

If the standalone tank is sharing a flue with your old boiler, you MUST make a change, since the flue would be ridiculously oversized for any tank type hot water heater on it's own, which would then result in copious acidic flue condensation, which will destroy the chimney from the inside out, and in the mean time it's at high risk of backdrafting. This all too common issue is called the "orphaned water heater" problem. (google it, or even search this side for it.)

The pumps come in a number of control modes, and will "know" when to raise or lower the power input based on the temperature or pressure feedback. A pressure-feedback pump using zone valves uses almost zero power when all the zone valves are closed (no zones calling for heat), even though it's pressurizing (at zero flow) the plumbing to the manifold. As more zone valves open up to allow flow it has to increase the flow to be able to maintain the same back pressure, and begins to use some real power (though much less power than an AC motor would need to drive the same flow at the same back pressure.)

Delta-T control drive modulate power up & down to hit it's programmed delta.

There are other smart pumps with other mode types as well. Take a look at the different specs for the Taco Veridian series pumps as well- they're not all the same.

Which one makes the most sense for your system depends on a LOT of other system parameters, and design choices on other factors often dictates the pumping modulation control.

Seriously, you won't be able to become Jr. Hydronic Engineer very effectively using this as a web-forum tutorial. Time to hit the books, decide your approach, run some preliminary numbers to verify that it works before you can really spec a pump. But it helps to know what the options are ahead of time.

 

[Matt Meier]

Dana,

I'm completely up to speed on the old hot water heater issues; I actually had to remove a chimney (or should I say breath on and watch it collapse) for an orphaned water heater when I bought my first house, so I'm sorry if I wasn't clear about having to replace it because of the atmospheric vent. I just haven't looked at my options yet, so I don't know what I'm doing for a new hot water heater yet. I haven't looked at the pros and cons of an indirect unit versus a combination boiler, or a separate on-demand unit. I'll get there in a few days.

I also promise that none of this is intended to be argumentative, nor is it an attempt for a shortcut. It's just that I tend to question everything, because I always want to know why, not just what.

That said, I understand what the ECM pumps do according to their modes of operation, and when I would use them according to common practice, as well as how they theoretically work in either mode. I did read one actual paper book (not John Seigethaler's, but one we have in the library at work), and walked through a number tutorials about topics like balancing and radiator emission. I'm actually shocked at how much I already knew from designing cooling systems and running thermal simulations. However, I'm afraid I may have gone overboard with how much I've thought about all this. Both pumping styles have advantages and shortcomings. However, I see a "problem" with delta-P pumping even when used with a zoned system, which is where most people recommend its use, and I can't find an explanation. Maybe I should re-pose the question to be more targeted.

Delta-P pumping is recommended by many people for zoned systems. However, the pumping method has a disadvantage in that the flow rate in a particular zone will remain constant, assuming that particular zone valve is opened. This causes a variable delta-T for the water in that zone as the boiler modulates the water temperature in the tank. We can solve this shortcoming of a dP-mode pump in a zoned system with very little effort, and by replacing a valve that we already are installing with something more flexible. Why don't we?

Perhaps your encouragement to run some real numbers is an attempt to make me discover, on my own, that it's just not worth the cost and effort. If that's it, then I'm sorry for re-asking. I'm going to do that this weekend once I take some more careful radiator measurements. I'll shut up now until I've finished a few test cases.

Thanks again for everything.

Matt

 

[NY_Rob]

...Delta-P pumping is recommended by many people for zoned systems. However, the pumping method has a disadvantage in that the flow rate in a particular zone will remain constant, assuming that particular zone valve is opened. This causes a variable delta-T for the water in that zone as the boiler modulates the water temperature in the tank.

That's the intended method of operation for a Delta-P pump/mod-con setup.
The DP pump maintains minimum required and ideal flow through the heat exchanger regardless of how many zones open or close.. and the boiler control unit modulates the fire rate based on supply and return temps and a constant/fixed flow rate. It's pretty much the same as a how fixed speed pump would work in the system, except the fixed speed pump is over/under pumping most of the time and probably makes more work for the boiler because of the varying flow rate.


For your domestic hot water- many think that for average residential use on a mod-con system- an indirect storage tank is the way to go. It has many advantages over stand alone and combi units, and it's brain dead simple to install/use.

 

[Matt Meier]

It's specifically the design of the delta-P pumping style that was making me question it. It's lacking in the sense that it always provides the same flow, regardless of the boiler's operating point. This article, specifically, got me wondering about the issue a little deeper:

http://www.achrnews.com/articles/128199-german-water-how-flow-rate-affects-heat-output

Now that I've looked at a few real numbers for my house, I'm even more convinced that this is a place where we could make significant improvements by adjusting the way systems are set up. My hypothesis is that we could make a noticeable improvement in overall system efficiency by using an integrated control system that takes the following inputs and generates the following outputs:

Inputs
outdoor temperature
zone return temperature
room temperature (the system needs to measure the transient states to see how quickly each zone heats, not just the steady-state temperature)

Outputs
hot water temperature
pump speed
valve position

Valve position is something that may or may not help things here, but this DOES require modulating valves. The benefit may be outweighed by the increased cost, but variable valves are an item that shouldn't be significantly more expensive than the current on/off valves. The cost is likely due to low demand. I'm further curious about the system being able to properly balance itself, using some intelligent control. I suspect this could be a useful tool for technicians, as the more I read the more I see that unbalanced systems are a constant headache.

I'm really busy this week, but next week I'm going to set up a Simulink model (or maybe VHDL, or something like that) to simulate a simple house with a handful of zones, to see what happens when switching from a blind delta-P or delta-T method to something that's completely integrated, and then later something that's self-adaptive.

I do need to know something that I haven't been able to find. I can't find the operating point where turbulent flow starts in a cast-iron radiator. Of less concern is the flow-through point (my own term), where the water enters so fast that it just runs right through the bottom and out the side, with little transfer to the columns. However, I'm concerned that the simulation will settle on a minimal flow rate and maximum delta-T, which may be in the laminar flow region. Does anyone have an idea about where that might be?

I've also seen some say "cast iron needs less than a 30° temperature drop to work", but nobody has been able to say why yet, and I'm concerned that's a rule-of-thumb number that's just stuck in people's minds.

Matt