Hard to beat the heat capacity, efficiency of water compared to air...3500 time better, and line size, wow! Hard to come up with HR disadvantages.

So according to John here are the options,

Hydronic Options:

• Electric (resistance, air-to-water heat pump, geothermal water-to-water heat pump).

• Natural gas or propane.

• Fuel oil/wood fired boiler/pellet fired boiler (itʼs possible, but a very hard sell based on current fuel cost, fuel storage, venting, efficiency).

Mod-Con Boiler - Shown on pg 24 for gas...."Modulating Condensing Boiler". Mod part: the boiler measures the outgoing water temperature and the return water temperature and decides how much gas it needs to burn. Old cast iron boilers had no regulation, even on mild days gas burned full blast and allot was lost to the chimney. the condensing or ''con'' part of the name. Con part: Condensing, these boilers purposely utilize as much heat in the transfer from fire to water as is possible. There is not enough heat left over to make a chimney work. They use plastic exhaust pipe going out the side of the house (usually), and a blower to force the exhausting of the boiler. With so little heat left in the exhaust condensation occurs. But thats okay, because these boilers were designed to do just that. The condensation is a kind of ''proof'' that the boiler is operating as efficiently as possible, squeezing all the heat out of the combustion process as it can. Given that this technology can shave 1/3 to 1/2 off the gas bill, which would you prefer. A cast iron boiler or a mod-con boiler? From what I understand about rocket mass heaters there is a phase change from gas to liquid that condenses of the exhaust pipe (sometime horizontally) embedded in a concrete mass couch where the heat is absorbed and slowly released into the night: That is why they are so efficient and burn almost 100% clean with no smoke. Sure take up a lot of floor space though, I’m thinking the same thing can be done in a wall.

  My HVAC background is from a different industry so I guess the electrical resistance type boilers are regulated by a water temp sensors-to-electrical that change the voltage to the heating element inside the tank.

The buffer tank levels off pressure spikes? The high mass uses an air chamber at top? Don't try this with a water heater, why?
-->

Wow. A lot to digest...but a few comments.

Disclosure: I ripped out an oil-fired baseboard hydronic system and retrofitted a ducted HP system in a 1960 house.

I am focused on HP (mostly ASHP) driven systems. I think that electrical-fired systems are 'future proof' for the coming 'energy transition', which I think will involve a net decrease in the costs of RE, but might ultimately have some wild changes in TOD rates. I.e. Dana's high PV penetration future starting in 3-5 years in most markets

I think the current green builder focus on mini-splits is driven by a combination of available tech (not a lot of Air to space heating hydronic in US), and the fact that conventional split ASHPs in the US are still 98% dinosaur-tech, with lousy SCOPs in the field (<2). There is no tech reason (IMO) why minis are the 'it' solution....lots of clunky multiple heads, poor zoning, aesthetics, etc. Great for a high-rise apt in Tokyo or Hong Kong (the original market), but a less than ideal fit for the NA market.

Moreover, I assume:
--solar thermal IS dead. Despite being pushed by boiler manufacturers, mostly in Europe. It will be very dead in 5+ years.
--high temp radiation is a white-elephant....too much of a COP hit for my desired HP-driven future system.
--traditional high-mass radiant heating seems problematic in current house with high performance envelopes. What about the future?

Imagine a world with high RE electricity penetration, with very low TOD rates during PV production hours, and something closer to current (or even higher) rates when the sun goes down. I can shift many appliance loads and my HPWH loads to the daytime TOD rate. No problem. But what about space heating?

With my current system (conventional split ASHP), I would use my house as a thermal battery....crank the heat up as soon as the TOD rate dropped, and try to store enough BTUs to carry me for 24 hours. In principle, in mild weather (>40°F) this would be easy, might have to overheat my house a few degrees. In colder weather, the house would be too hot at bedtime or too cold during breakfast. I would have to limit my use of the thermal battery based upon comfort decisions.

What would new construction look like in such a scenario? A PH or a PGH might be fine with an air-supplied ASHP source, and have a long enough cooling time to just fire the space heater on a 24 hour cycle without comfort issues. I think this will be part of the value proposition of such high performance homes in Dana's RE future. Not that the energy bills are proportionately lower due to high R-value, but that the thermal relaxation time is long enough to heat exclusively with (grid delivered) very cheap PV power, without comfort issues.

Poor grannies (in 2030) won't be freezing in their under-insulated, HP heated houses, they be warming up during the day, and freezing at breakfast time waiting for their smart thermostat (retro-styled to look like the Nest) to turn on when the TOD drops. That's progress I guess.

So, back to the OP question....what role hydronics? An obvious utility of hydronics is thermal storage. If ASHPs to water units became widely available (likely), you could imagine having a large hydronic thermal battery to provide cheap BTUs during the breakfast-time period. Alternatively, high-mass radiant like systems might make a comeback, not because they are warm on your toes, but because they would allow diurnal BTU storage (with a decent envelope) at low HP delivery temps.

In a PH or PGH both of these options would likely be unnecessary, and add unneeded complexity. So, in a future dominated by a fleet of PH or PGH stock, I don't see hydronics having any value.

But, blasphemy, lets consider a different scenario for 2030....we get something like Dana's future scenario with cheap/free daytime power and expensive night-time power with something resembling the current NA housing stock, whose envelopes are too poor to allow the house to provide comfortable thermal storage. We can suppose these have been/can be affordably retrofit to 50-70% the current average space heating needs per square ft, but no better. Then, can we imagine a marketplace for hydronic thermal storage systems?

IOW, I say that my company will get you 100% PV derived space heating (a selling point for middle aged millenials), at super cheap TOD rates (ditto), in your existing house built way back in 1994. I just need a storage unit maybe a little bigger than existing fuel oil tanks, and an Air to water HP source (which could even be single speed/cheap, sized to provide daily BTU load during the 8 hour PV window). The homeowner doesn't care about how it works, but it does. They have a legacy oil (or more likely increasingly expensive gas) heating system with hydronic radiation, (baseboards or underfloor), and my company removes their boiler and legacy oil tank (if they have one), and puts in the hydronic storage tank where the oil tank used to be. The new system includes a minisplit to provide/supplement the heat during the day (since radiation temps are low compared to their original purpose), and provide summer AC. The primary hydronic system could also provide some radiant cooling, provided that the mini-split was designed to control the interior latent loads. (if you don't like this idea, heck, its 2030, those old baseboards would have tiny wireless sensors retrofit that warn the central control if the radiation is getting too close to local dewpoint).

In a 2030 house with a legacy gas furnace and AC with ducts...I put in the same air to water HP and big tank, with a hot or cold water to air coil in the air handler.  Easy.

Numbers: a 300 gallon tank with a 40°F swing stores ~100 kBTU.  Say my legacy house drops 7°F below setpoint overnight (form being a couple degrees above at sundown), I need 70kBTU to do a 5-7°F recovery while the family is in their warm beds, they wake to a warm house, and the tank provides another 30 kBTU to maintain setpoint until the TOD drops at 10AM.

IOW, when we look at residential HVAC systems in 2030, I do not expect every house to be PGH with 1 or 2 minisplits. I expect a lot of systems that may not currently exist, which are optimized to provide cheap RE-derived space heating to our current housing fleet, which has been subjected to quality energy retrofits and airsealing, but not to anything like a PGH or PH level of performance.

I agree, air to water heat pumps make a lot of sense. Preferably with low mass radiators + water tank storage. Combined with tight houses, slight positive pressurization and dehumidified ERV air, radiant cooling can work.

If you can't make AC work, then hydronic is considerably less attractive (except in places like the UK - ~93% hydronic).

Woodgeek68, thanks for your post. Can you please explain some of the abbreviations since not everyone reading your post is a pro.

HP
ASHP
RE
TOD
SCOP
HPWH
PH or PHG
IOW
COP

"So, back to the OP question.." Only question I had so far didn't get answered. In my second post what is the purpose of the buffer tanks?

The intent of this thread is to review John's white paper starting with history and the evolution of hydronics by pro's such as yourselves that help the non-pro understand in simply terms, my bad for not making that clear in the OP. Compare it to some of the other popular options. I'm not sure I agree with the mini-split wave and moving air around to load mass poorly, and I see people calculating their efficiency and load requirements without considering this. As John said, air has 3500 times less heat capacity than water, therefore, it is a poor convector to carry heat from one location to another. I watched a video over the weekend of a tight home built in NM hot desert that uses NO AC in 100+ F summers, no heating system, completely off grid, city water and sewer, no hrv humidity control required the mass walls does that naturally, that went far beyond green PV panels on the roof with minisplits blowing air around at 1-2 locations in a tight envelope. House did use a JAP way to make a room look and feel larger tho. 2. 5 hours long but takes you trough the entire DIY build process. These real live builds(and there are many more on the internet) prove the steady state r-value calculations and load calculators being thrown around this site at random inaccurate! This is probably your 2030 home and no one system will fit all, not only will the need for grid power go down but so will the need for HVAC putting the need for those industries out of work including Japan and China once NM(North America) learns how to design to natural mass as well as they have. I have seen other builds in zero degree weather that never got below 65 F from well designed solar mass, last winter as harsh as it was.

https://www.youtube.com/watch?v=Z3Cvqxkqwr4&list=PLvuQjrubeFM0rbcsU6zHs1bdCzDKS-uq-

That is all getting a little ahead of the white paper review I'll keep posting on little by little so it does not get confusing to the average reader.

The primary driver/advantage of residential hydronic radiation, capacity and comfort, are rapidly disappearing with the improvement of thermal envelopes. When you have a shoddy mid 20th century envelope, you need to move a ton of BTUs, and you can get noticeable temp and radiation gradients. Moving and mixing that much heat with air is tough, and leads to 'drafts', stratification, etc.

At the BTU/h.sqft loads of post 1980s code construction, in all but the most extreme climates, a whisper of air supply leads to a quiet, draft free heating source (unlike clicking or banging hydronics) with no detectable gradient. So the rationale for hydronics is not just going, its gone.

Check out the data on heating systems in new residential construction from the gov. Hydronics are used in ~2% of new construction homes in the US!
http://www.census.gov/construction/chars/pdf/heatsystem.pdf
Even in oil-fired NE, its only ~10% of new construction. Presumably much of this remainder is radiant, not baseboard.
Part of the trend is, contra your suggestion, the increasing prevalence of central AC.

I'm sorry you didn't like my whimsical imaginings....I was trying to find a role, any role, for hydronic systems in future residential systems. Its hard to invent one, and then it is mostly for legacy systems (that already have boilers and hydronic radiation).

I like minisplits in concept, but like you am skeptical that in 20 years we will have most existing houses heated with them. Unlike you, I think we will eat the 10% blower losses, and ducted ASHP systems (with inverter driven compressors) will predominate, in a housing fleet that has far better insulation and airsealing than the 20th century standard.

I am also skeptical of arguments that consumer purchases will be driven by physical constants, such as the specific heat of the heating carrier fluid. I could argue that coal has much higher energy density per volume than natural gas, but for residential heating, gas is >50%, and coal is <1%. What gives?

I'm not a pro...

HP: Heat Pump
ASHP: Air-source Heat Pump
RE: Renewable Energy, typically Electricity, solar or wind or hydro.
TOD: Time of Day rates, or TOU, Time of Use rates.
SCOP: Seasonal Coefficient of Performance, or COP averaged over a heating season, sometimes including backup.
HPWH: Heat Pump Water Heater, e.g. the GE geospring unit.  Pumps space or ambient heat BTU into a DHW tank with a COP ~2.3 or higher
PH or PGH: Passive House or Pretty Good House. The former, PH, is a superinsulated and super-airsealed structure whose space heating needs are roughly 1 BTU/sq.ft*HDD, where HDD is heating degree day.  The latter, PGH, asserts that PH insulation levels are not optimal, and amounts to roughly 2 BTU/sq.ft*HDD. (for comparison, mid-20th century housing stock runs >10 BTU/sq.ft*HDD, current best codes are more like 5.)
IOW: In other words
COP: Coefficient of Performance, that ratio of Heat energy delivered by a Heat Pump, in heating mode, to work energy consumed by the pump.  Typical values are 2-4 depending on the situation

As for the buffer tank....unlike old-school boilers that had output power in excess of that required to run DHW, new, lower output (often mod-con) boilers do not.  That is, a shower might need 100 kBTU/h water heating, two showers at the same time...200 kBTU/h, versus the 20-30 kBTU/h design space heating load for a modern envelope.  So, you store 2 showers worth of hot water in a well-insulated tank, and the boiler can recover the tank in <1 hour after the showers are over.

Got it, thanks woodgeek68. Makes me laugh, last time I posted on a blog over @ GBA on an idea I had to integrate a minisplit HRV/ERV ducts/plenum, small blower, sends/returns, to solve the closed door temp drop issues some are seeing to large, Martin got on me for acronyms the newer readers may not understand, although to me very common. You got me beat, I learned a few up there. I think as we get better at this we forget about the new people out there. I know when I first started I had a list of them. He also said on a DHW blog heat/cooling integration is a subject of the largest amount of controversy and discussion. I thought John did a great job on this report, I just printed it out its THICK! so I can see it better. I'll take the time to look at it, the history, the end looks like the most interesting part and draw conclusions then. Thanks for the input. Lots of opinions on HVAC integration. I personally tend to take a close look at the tighter mass solar net zero or positive builds, not mainstream construction or statistics. NM no AC house I posted above generates positive storage while the neighbors are at peak grid mid summer desert 100+F days. At the same time I too need to look at retrofits since my company does them. I am looking at some new materials coming to the US for that I think will take the loads way down at an affordable cost.

Buffer tanks?

http://www.borstengineeringconstruction.com/Buffer_Tank_Design_Calculator.html

…and read the instructions on why they may be needed and use the software to properly size them. Siegenthaler clearly explains how to properly install them, in addition to how to size them (which was the basis used for this software), so no need to cover that too.

Terry,

You have stated: "All “net-zero” houses will use solar PV system, and thus favor an “all electric” HVAC system."

Many houses such as those built with NREL as consultants are "net-zero source energy houses." There is no reason that these need to be all electric houses, since source energy allows conversion between energy sources. Coal is the predominate fuel for electrical generation in this area, so the local conversion factor is even worse than the national average. The cost of natural gas per unit energy in this area $0.024/kWh compared to electricity at $0.118/kWh, so even with an average COP of 2.3 (hard to achieve that high in this area), gas is cheaper by about a factor of two in producing thermal energy with a high-efficiency furnace.

Tight, energy-efficient homes typically require heat recovery ventilation (HRV) systems. Forced hot air ducting provides an ideal way to incorporate HRVs into houses, but this approach is not possible with hydronic. Please add that to the disadvantages of hydronic systems.

In a similar vein, whole house humidifiers or dehumidifiers can use the same ducting as the heating system for forced hot air, but cannot be easily incorporated in houses with hydronic systems. Please add that to d

All such comparison are irrelevant until we know the climate of the building site. When building in the mountains cooling is rarely a factor and hydronic heating is of little use where the predominates load are latent. Here in Minnesota it is just best to be somewhere else in July/August and Jan/Feb.

Looks like we have some more pro's chiming in, sweet! :) I went back and reread all the post now that I understand the HVAC pro lingo and updated the list. I found some other hydronic disadvantages according to Martin Holiday added too. Let me know if they need correcting. John has several hybrid solution options in his conclusions I'll look at and ask your help with later, I think may work in any climate zone, check them out.

I don't got a lot of time to correct typos so hopefully you get the idea :)

Considerations

 

• Small design heating loads in the range of 10 to 15 Btu/hr/ft2. (A 2000 ft2 house at 10 Btu/hr/ft2 is only 20,000 Btu/hr design load). Low water temp to coil (IE: 120F)

• Monthly service charge associated with gas meter may be hard to justify based on fuel cost difference and usage. (consider “all electric” house).

• All “net-zero” houses will use solar PV system, and thus favor an “all electric” HVAC system.
• Hydronics is the “enabling technology” that underlies all thermally-based renewable energy systems.
• It doesnʼt make sense to focus solely on high efficiency space heating, and ignore the potential for high efficiency domestic water heating. Some homes incur ⅓ cost of heating for DHW. Minisplit and forced air needs separate system. Average DHW 30% of Heating load. Identifies a need for integration minisplit and forced air does not provide.

·        Hydronic Retrofits. may provide client ROI options if the required heating loads can be dropped substantially. Storage in concert with future low cost PV-Hydronic-ASHP could provide high COP/ROI’s worth investing in depending on the clients existing legacy systems and lifestyles.

·        “All electric” PV homes of the future will depend on local domestic utility gas/electric company supply cost.

 

Advantages of Hydronic

 

• Simple room-by-room zoning is possible with many heat emitter options. Donʼt have to leave all doors open for internal heat balancing. A limitation of single point(minisplit) heat/cool delivery such as wall cassette.
• Easily adapted to renewable heat sources. (solar thermal, hydronic heat pump, off-peak)
• In some cases a single heat source can supply heating and DHW (fewer burners, less vents, less fuel piping)
• Electric heat sources and water-based thermal storage is easily adapted to “off-peak” or coming “smart meter” rate structures. (thermal storage hardware already available)
• Utilizes thermal mass by direct feed vs air.
• Radiant heat is more comfortable than forced air.

Disadvantages

 

·       Solar thermal systems generate a lot of energy in the summer, far more than you need. But you can't really store it and put it away for the winter very easily. With a grid-tied PV system, you can sell the electricity that you don't need. You can buy it back when you need it in winter. This makes a watt of electricity a LOT more valuable than a watt of heat.

·       Solar thermal systems have lots of piping, valves and pumps. More mechanical parts therefore potential for higher maintenance compared to ASHPs (eg: minisplits).  Keeping in mind that minisplits can be high maintenance too.

·       Martin Holladay concluded that solar thermal is”dead”  "unless you’re building a laundromat or college dorm, solar thermal is dead." That's an overstatement; there are many southern, sunny parts of America where it makes a lot of sense. But with the continuing drop in the price of photovoltaics, the ability to tie them into a much bigger system, the increasing efficiency of electric heat pump water heaters and the simplicity of having just one solar system instead of two, I wonder if solar thermal hot water heating is still hot.

·       Higher installation cost due to more parts and assemblies.

·       Systems that rely on high mass (floors, wall, mass) can over heat if improperly designed. There are no design guides that are effective at doing this in all climate zones, so its’ hit and miss.

·       Tight, energy-efficient homes typically require heat recovery ventilation (HRV) systems. Forced hot air ducting provides an ideal way to incorporate HRVs into houses, but this approach is not possible with hydronic

·       whole house humidifiers or dehumidifiers can use the same ducting as the heating system for forced hot air, but cannot be easily incorporated in houses with hydronic systems

 

 

HVAC Pro Acronym’s : (if you’re not a pro, you can look like one using these ;)

 

HP: Heat Pump

 

ASHP: Air-source Heat Pump

 

RE: Renewable Energy, typically Electricity, solar or wind or hydro.

 

TOD: Time of Day rates, or TOU, Time of Use rates.

SCOP: Seasonal Coefficient of Performance, or COP averaged over a heating season, sometimes including backup.

 

HPWH: Heat Pump Water Heater, e.g. the GE geospring unit.  Pumps space or ambient heat BTU into a DHW tank with a COP ~2.3 or higher

PH or PGH: Passive House or Pretty Good House. The former, PH, is a super insulated and super-air sealed structure whose space heating needs are roughly 1

 

BTU/sq.ft*HDD, where HDD is heating degree day.  The latter, PGH, asserts that PH insulation levels are not optimal, and amounts to roughly 2 BTU/sq.ft*HDD. (for comparison, mid-20th century housing stock runs >10 BTU/sq.ft*HDD, current best codes are more like 5.)

IOW: In other words

COP: Coefficient of Performance, that ratio of Heat energy delivered by a Heat Pump, in heating mode, to work energy consumed by the pump.  Typical values are 2-4 depending on the situation.

 

HDD: Heating Degree Day

 

DHW: Domestic Hot Water

 

PV: Photovoltaic – A form of “renewable” solar electric energy  Materials presently used for photovoltaics include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium gallium selenide/sulfide.

 

Solar Thermal: Evacuated water tube heat pipes that supply HR systems.

 

HR: Hydronic Radiation (heat source)

 

ROI: Return on Investment

 

 

Definitions

 

Buffer tanks: “low mass” zoned heat sources can short cycle system when all zones are not working, the heat source via boiler or burner put out more heat than the emitter can store and short cycles. Applies more to gas systems, although electrical systems are not as affected by short cycling can fatigue components. A storage-buffering device for peak heating and DHW loads.

 

Mass – a material of a certain heat storage capacity (IE: water, air, concrete, earth, drywall, etc) . Dependent of density, specific heat, and mass(weight). A low mass example would be a wall emitter that has little storage capacity and emits fast. A high mass example would be home full of interior uninsulated walls and floors or a mass heater made of earth or concrete. Mass can be loaded by solar or HVAC.

 

Emitter – Mass that stores and emits heat in a certain lag time. The lag time can be used to shift heat loads off peak utility cost if grid tied. Lag time is difficult to design to.

If we address space heating exclusively the comfort and economy of hydronic heating is unmatched and the building envelope is of little consequence until we get to passive house standards. Once there we can argue the economies of super-insulation and triple pane windows.

I design HVAC systems all over N.America both new construction and old without compromising comfort or economy. There are those who question the cost of such systems, but the matter of "worth" is clearly an individual precept.

I design forced air systems and integrate them with radiant heat on a regular basis hear in Minneapolis where the weather is extreme, in all seasons, by all standards. It is not a "crap shoot", rather applied science.

Try to spot-heat 8 rooms on three levels with mini-splts as I do with my radiant floor system.

Forced hot air ducting provides an ideal way to incorporate HRVs into houses, but this approach is not possible with hydronic.

According to references such as this one, combining ducts is only ideal from an initial cost standpoint and otherwise it is best to have a dedicated HRV supply and return to each room. Then it can always be correctly balanced.

Posted By jonr on 04 Jun 2014 10:49 AM

Forced hot air ducting provides an ideal way to incorporate HRVs into houses, but this approach is not possible with hydronic.

According to references such as this one, combining ducts is only ideal from an initial cost standpoint and otherwise it is best to have a dedicated HRV supply and return to each room. Then it can always be correctly balanced.

+1 on that!

The cfm requirements for heating & cooling are an order of magnitude higher than that for HRVs, making heating/cooling  ducts ridiculously and sub-optimally oversized for ventilation-only.  When using heaing/cooling ducts for HRV it generally requires running the heating/cooling system air-handler at least on a duty cycled basis to guarantee sufficient mixing & ventilation air in each room, which doubles or triples the energy use of the ventilation system.

Exactly so. I use ERVs for bath exhaust and balance flow in all systems. The fresh air may go into a forced air system common for upper floors with AC loads from big glass, but for hydronic homes without AC and ERV or HRV is the exhaust and IAQ devise.

Right, the only duct work in an energy efficient home these days should be just for the required ventilation via ERV/HRV.

Posted By Dana1 on 04 Jun 2014 11:07 AM

....When using heaing/cooling ducts for HRV it generally requires running the heating/cooling system air-handler at least on a duty cycled basis to guarantee sufficient mixing & ventilation air in each room, which doubles or triples the energy use of the ventilation system.

Why is that required for "sufficient mixing?" My HRV dumps into the air return of my zoned GSHP ductwork. With no zone calling for heat (most of the time), all zone control dampers are open, and the air flows to every register in the house, without the heat pump blower running at all, as far as I can tell.