Hydronic System Design & Boiler Piping/Control

[sorrentino100]

Ok, we are installing a new heating system in a rental property. The old unit was an oil-fired boiler with fin-tube baseboard convection. That system was vandalized, so we start from scratch.

We are installing a gas boiler; initially propane and then to Natural Gas when the gas utility gets around to installing the gas line from the main to the house.

The home is on a slab. We are planning to utilize Viega FostaPex (Pex-Al-Pex) in a series loop configuration for each zone (2). We don't want to trench the slab, so we are open to suggestions as to the best way to run the pex tubing.

The boiler will be a cast iron New Yorker CG-D Series 20 boiler. It's rated at 37.5 BTUH 31K AHRI & 27K IBR. 82.3% Efficiency. 2.5 gallon water content. Has pre- and post-purge control. It will paired with a 50-gallon BoilerBuddy buffer tank and a SuperStor 45 gallon IDWH.

The home has a calculated heat loss of 24,672 BTUH. It will be split into 2 zones; one for the living, kitchen and dining room areas (Zone-1 13,775 BTUH) and bedrooms and bathroom (Zone-2 10,897 BTUH). Programmable thermostats will be employed for each zone. Zone valves will be employed for each zone.

Design temp is for 72-degrees on a 10-degree day. Average water temperature is 140-degrees @ 1 gpm. Zone-1 flow is 1.46 gpm and 10.32 ft head; Zone 2 is 1.06 gpm and 9.6 ft head.

An outdoor reset control will also be utilized. As this will result in return temperatures below 130-degrees at certain times, we'll need a way to control the return temps and keep them above 130-degrees. We understand Taco makes a 4-way mixing valve (IO75T4R-1) to accomplish this and Tekmar makes a 402 control which would control a mixing device, zone valves and allow for separate IDHW control utilizing different supply and differential for both the boiler and IDHW. We believe you must use Tekmar thermostats to work with this controller.

We'd appreciate a few things:

Comments on this design and ways to implement it. We don't want to install a mod-con boiler due to initial cost (~ 3K vs ~1k), life expectancy, reliability and maintenance costs.

A way to calculate how to size each successive fin-tube convector as water temperatures drop in the series of convectors. The sizing in the attachment is based on 140-degree average temperature with no consideration for diminishing temperature as the water travels in series.

A schematic diagram of this layout, if someone has a program to do so, so we can provide it to our installer.

I'll try uploading the floor plan and fin-tube convector sizes and location. Z2 R1 is Zone 2 Radiator 1 (the first in that zone series). Scale is 1/4" = 1'.

Thanks!

 

[Dana]

Where is this located, what does gas/electricity/propane cost in your area, and who did the heat load calculations?

By the time you've added in the cost for the Boiler Buddy system design & zone controls you may be north of $10K right now, then have to pay for the natural gas hook up & conversion later. Depending on climate and local utility costs you may be better off heating & cooling the place with a 2-4 head 2-3 ton ductless heat pump. (Multi-split/mini-split). The operating costs are competitive with natural gas in most places, the upfront cost will likely come in lower than what it costs for your hydronic solution, and having high-efficiency air conditioning can be a selling point.

If the heat loads of the bedrooms in your sketch are real you can probably install a single 3/4 ton or 1-ton mini-duct cassette to manage those three rooms with ultra-short duct runs, and maybe a 1-ton mini-duct cassette or a pair of half-ton wall units for the kitchen & living room.

The better versions all modulate with load, and are whisper-quiet- quieter than your refrigerator and deliver extremely stable room temps.

 

[Sponsor]

 

[Tom Sawyer]

82% running propane? Hope ya got a big fat wallet.

 

[Dana]

82% running propane? Hope ya got a big fat wallet.

I think he's just looking for a TENANT with a big fat wallet.

Don't wait for the gas grid to come to you, and don't buy a propane burner. Ductless (and modulating mini-ducted) heat pumps are getting better and cheaper every day. I don't sell them, install them, nor do I have one in my house (I'm already on the gas-grid), but the financial reality is that they're cheaper to install than hydronic heating systems, and cost a heluva lot less to operate than propane & oil. (You could buy the ductless system twice over for the difference in operating cost over 5-6 years.)

Neither propane nor oil are never going to return to being cost-effective. (Maybe in 2o years, after most people in developed countries are driving electric cars it might be.) It costs between $75-100/bbl to cook the bitumen out of oil sands or frack shale for the lighter oil. It takes many times more wells to get at shale oil, and those plays all crap out in under 3 years- it's a drilling-schedule nightmare for the major oil companies. The Arctic oil exploration is similarly expensive and risky, though if they can pump for 20 years at $100/bbl it might eventually pay off.

The OPEC countries can (at least for now) make money at $30/bbl, but the amount of upgrading it would take to get their volumes up to match the world demand would also require an oil price well north of $75/bbl. Since there is risk to those capital expenditures and they can meet their national budgets (and then some!) with the pumping capacity they have, there is no incentive for them to increase capacity. Without investment in more capacity, the price of oil can only rise.

While crude has been falling in price slightly in the US in recent months, it's at a price where some oil plays are simply not profitable. There is only so much cash the major oil companies can afford to pack down a frack hole and they have started to cut back on that insane capital expenditure, since they can't actually make money at it.

The story for natural gas is somewhat better, but not for propane. A the current price for natural gas they aren't even breaking even on the gas with shale gas, but with the high price of propane they can. Roughly half the propane in the US is derived from "wet gas" wells, the other half is a by-product of oil refining. "Dry gas" wells don't make money unless it's from a traditional gas source- the tight-gas resources (from shale, or coal-bed methane) only make money on the liquids fraction, the propane/butane, etc. As the oil majors pull back a bit from shale-oil, the oil refining volumes decrease, and the propane supply tightens, which raises the price of both propane, and to a lesser extent the price of natural gas. At 1.5-2x the current price gas is pretty profitable even from dry-shale and coal seam sources, but that won't help the propane price at all. Natural gas would have to triple or quadruple in price to be as expensive as oil or propane, but it will never get there.

At $75-100/bbl oil electric cars are viable to those who can finance the hefty upfront cost for batter pack big enough to give them a reasonable amount of range, and a charging system to charge overnight at home. The price trajectory on those batteries appear to be fast enough that they will cost half as much in 2020 as they do now, a price point at which point there could very easily be a paradigm shift where a large fraction of cars sold would be electric. If that happens VERY quickly (faster than anyone actually believes) the price of oil could crash for awhile, or maybe forever, as the rest of the world makes that transition. China is now the largest market for new cars, and for local air pollution reasons and balance of trade reasons they have begun a push for car-charging infrastructure to be installed around the major built-up cities, which will accelerate the battery cost drop, even though most cars sold there would still be gas or diesel powered. How far & fast they push that program over then next decade will probably make or break the major oil companies, and OPEC countries will have to adjust their budgets for when the oil price crashes. When oil crashes, the price of propane will fall with it.

Even if the oil price disruption happens before 2030, it's almost certainly not going to happen before 2020. You can buy a lot of heat pump & electricity with the difference in heating cost between ductless heat pumps and propane/oil burners over 5-10 years.

This isn't idle speculation on my part- it's what the investment banking sector has been saying for a year or more. Sometime the banking sector's prognostications become self-fulfilling prophesies: If they won't invest in shale oil infrastructure, the cost of that capital expense soars, making production stagnate or fall, etc. As recently as this week Kepler Cheuvreux (a European investment bank) published a piece of analysis showing that even if the power grid were supplied completely with new-wind & new-solar (at somewhat inflated costs for those sources of power) that it would provide cheaper transportation energy where the rubber meets the road with electric cars than diesel or gas cars with oil that costs $75-100/bbl to produce. Actual grid power is cheaper than that today.

In the face of ever cheaper renewable energy & cheaper electric vehicle batteries oil as a transportation fuel will eventually decline. But until it does propane & heating oil won't decline to the affordable range of decades past. Oil only became more expensive than natural gas about 10-12 years ago, but averaged over the past 5- years it has been 3x as expensive, with no real relief in sight, and the story for propane is only worse.

 

[Tom Sawyer]

I don't think we will see a big increase in either propane or oil prices this year and maybe not for the next five years or so. US oil production is currently outstripping Saudi Arabia's, but like anything, it won't last. Propane, because it is a derivative of crude oil will always be expensive. You get a break on the price if you use a crap load of it but if you use that much the bills going to be astronomical anyway. I like mini-splits. We sell quite a few of them and they get more efficient every year which, kinda pisses off folks that bought theirs a couple of years ago, lol. Beware though that ducting one in an older home can get very pricey. Once the insulation and wallboard are in place, getting ducts where they need to go is a bit of a challenge.

 

[Dana]

I don't think we will see a big increase in either propane or oil prices this year and maybe not for the next five years or so. US oil production is currently outstripping Saudi Arabia's, but like anything, it won't last. Propane, because it is a derivative of crude oil will always be expensive. You get a break on the price if you use a crap load of it but if you use that much the bills going to be astronomical anyway. I like mini-splits. We sell quite a few of them and they get more efficient every year which, kinda pisses off folks that bought theirs a couple of years ago, lol. Beware though that ducting one in an older home can get very pricey. Once the insulation and wallboard are in place, getting ducts where they need to go is a bit of a challenge.

US oil production is only outstripping Saudi Arabia's because the Saudis have cut back production to keep the world price up, and the fact that the US oil companies had in prior years invested heavily in tight shale oil production. At the current $90-95/bbl many of those shale plays are actually losing money on every barrel, others are offering too low a return to cover more junk-bond type debt service for continuing to drill, which has resulted in the companies cutting back on drilling. A typical tight-shale well produces something like 95% of the oil it will EVER produce in the first 2-3 years, so US production is all but guaranteed to fall off in the next 2 years (barring a major round of drilling investment in 2015.) By the end of 2016 we should be seeing the current/recent slack-off in drilling investments translate in to higher WTI-Cushing oil prices.

The shareholders of the oil companies simply demand higher returns than what they can make from shale-oil at $95/bbl, but it's not clear where the oil companies are going to do better, other than to make their legacy oil plays operate more efficiently cash-wise. That will increases their gross margins, but does not increase the supply of oil. Shale plays have been pretty bad for the balance sheets of the oil companies- their stock price can't afford for them to stay on "drill-baby-drill" hamster-wheel fields where wells crap out in under 5 years unless the price goes substantially higher.

The current price has very little room to fall, but plenty of room to rise over years, and over the anticipated lifespan of a boiler it's likely to go up another 30-50% before the efficiency and fuel-switching these high prices stimulate cut significantly into demand. The wild card in all of it is how rapidly electric cars take market share in the developed world, which can also cut significantly into crude oil demand, but nobody is predicting that to have much affect until at least 10 years out.

A pretty-good analysis of different scenarios of how this might play out is found here. (That's 130+ pages of banker-speak & pretty graphs, but it's worth reading more than just the executive summary. Their critique of IEA's oil market projections seems valid, but their projections on the actual costs of renewable energy sources are way too conservative- demonstrably 50% too high in the case of PV.)

Multiple mini-duct cassettes can be a lot easier to retrofit into older homes than fully ducted centralized systems. If you look at the layout & heat loss estimates attached to the original post this would probably not be a very difficult house to retrofit with 1-2 ductless heads ( or a single mini-duct cassette) for the kitchen/living room zone and a single mini-duct cassette with the ducts split into a star topology central to the bedroom zone. The bedroom zone cassette could even be mounted in the top of one of the closets.