Comparative efficiencies Hydronic vs. HVAC

Steve_35

it requires less electricity to move btus through hot water than hot air although the new PCM motors help reduce blower energy usage.

Other system factors that can increase usage with FHA are duct leakage, infiltration and exfiltration. The latter are brought about through imbalances between supply and return air.

In addition if you have an owner to whom filters are an un thought of item you will waste additional heating dollars.

The newer 2 stage furnaces while more closely matching building losses incur greater electrical usage due to the longer blower run times.

Mark Evans

Comparative efficiencies Hydronic vs. HVAC

I am researching an article that will appear in HPAC Magazine- a Canadian trade publication. As a participant in the heating and plumbing industry, I have long heard efficiency touted as a selling argument used to compare hydronics to HVAC, where hydronics are presented as the more efficient choice. I would like to know the science that supports these claims and use this in the article. I have asked Mr. Holohan for permission to post this as I want the motive for asking to be clear- I would like to be able to provide facts to support the claim. For those who reply, I will be including those postings of interest and giving an attribution as to the respondent and the source (The Wall). If you wish to be confidential, please reply privately to me at writemarkevans@hotmail.com

Thanks,

Mark Evans.

hr

That is a million dollar question

with no clear, industry accepted, answer. Studies conducted so far slant one way or another. It's a very hard thing to model or build and test.

As hydronic methods and equipment change and get more efficient, so does the forced air. Typically they, forced air, are a bit ahead of hydronics in upping the efficiency due to the size of their market.

The industry (hydronics) has been trying for years to agree on and find funding to complete this project. We need funding possibly from an ASHRAE, DOE, GAMA, RPA, TUV pool of talent and money.

Dave Springer from Davis Energy Group 530-753-1100, springer@davisenergy.com, a real nice guy, has some of the best data in my opinion, to date.

hot rod

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rb_6

DOE report worth a look

Energy Consumption Characteristics of Commercial Building HVAC Systems Volume III: Energy Savings Potential
Prepared by Kurt W. Roth, Detlef Westphalen, John Dieckmann
Sephir D. Hamilton, William Goetzler
TIAX LLC
20 Acorn Park
Cambridge, MA 02140-2390
TIAX Reference No. 68370-00

For Building Technologies Program
Project Manager:Dr. James Brodrick (DOE)
Contract No.: DE-AC01-96CE23798
July, 2002
_____________________________________________________

One of the graphs showing radiant ceiling cooling as having the fastest payback is shown at our blog.

jerry scharf_3

man that's hard to answer

Mark,

There are so many dimensions to the problem that it's really hard to tackle. As Hot Rod said, the results you find are very related to the experiment you build. I have tried to put together what I think is a balanced view of the issues that drive this.

Individual system implementation, both in design and implemtnation are the critical elements. A well designed and carefully installed FHA system will be more efficient than a poorly installed hydronic system.

Also, please note in your article the huge importance of the building envelope (insulation, air sealing, windows/doors.) In an ideal world, I would like to see every mechanical systems person being a strong advocate for a low loss builing envelope. The delta between FHA and hydronic is much less than a well implemented building envelope!

It can be clearly argued that hydronic systems can be more efficienct in the ideal. Water is a much better heat transfer media than air, and at the limit this will drive efficiency. This shows up in both the moving of heat from combustion to transfer fluid and from the energy required to deliver the transfer fluid to the environment. I think the biuler vs. furnace side of things is well established and dependent on system design as well as equipment choice. If you want more on that, let me know.

In the real world, the big killer for system efficiency is loss of heat in the transfer fluid. this happens 2 ways.

One is to lose transfer fluid itself. Since a leak in a hydronic system would (should) get fixed, one can assume for a properly operating hydronic system this is zero. For an air duct system this is a substantial problem. Leakage at the 1-2% level is considered a good install and poor installs can lose more than 10% of the heated air. That's just dollars out the window.

The second if from heat loss though the walls of the piping/ducting. Again hydronics can hold the edge, but it is unclear in practice.

Since the size of the pipe is much smaller than that of a duct and it's shape is more regular, it is cheaper and easier to gat good insulation levels on pipe. It is alse easier to minimize voids in the insulation container with some care (sadly rarely done.) For ducts, insulation is only fair for the duct runs themself (often lower than pipe insulation and a larger surface area,) and the junctions are typically just contact adhesive and exposed fiberglass stuck on. This is really a minimal insulation level given the realities of fiberglass insulation and this being a bad situation for it. People might say you can ignore the insulation level on the return ducting, but this is wrong. Since this is the air into the furnace, any heat lost in the return ducts needs to be added by the furnace. The thing is that this air is at a lower temperature and so the rate of loss through the insulation would be lower than the hot air side.

Fr the insulation loss, you have to also look at the tranfer medium temperature in use. Clearly low temperarture hydronic, e.g. gypcrete, warmboard..., radiant win hands down. Also, outdoor reset allows lower water temperatures compared to fixed point, which cuts down system loss. With baseboard heat in cold climates, you can be looking at water temperatures getting up to 180F or more. This will certainly increase the system loss. Theoretical differences between this and hot air at say 140F are meaningless, the installation details swamp anything that this can contribute.

hope that helps,

jerry

GMcD

Hydronic vs All-air

Start with the basic physics: thermal capacity: water can hold 3400 times more energy than air (specific heat) and you can flow the same amount of energy (Btuh) through a 3/4" pipe as a 14" round duct. So, advantage water as an energy transport method. Now extract that energy at the terminal end: most conventional systems like hydronic heat pump units and four-pipe fan-coils convert the hydronic energy to air energy, and end up blowing hot and cold air around for space comfort. Well, if you take that same hydronic energy and use it to create direct infrared heat exchange (radiant systems) you've cut out one step in the process, AND addressed the main component of human comfort (radiant) for a win-win situation - increased comfort, with lower energy requirements to do it.

The energy required to transport water (pumps) is also a lot less than the fan energy required to move the same amount of Btuh in a chunk of air.

However: a really well designed all-air system could still end up being more energy effcient than a poorly designed and applied hydronic radiant system in the exact same house. The reality is that there is still a lot of mediocrity out there on both sides so there is no way to directly compare installed systems types unless you are doing some heavy duty computer modelling with a common "base building" design and some good software that actually models radiant and "resultant" space temperature (most, if not all commercial North American building simulation software is still built around "air" temperature as the solved variable- the exception would be the TRNSYS program from U Wisconsin).

The science you are looking for starts with basic specific heat capacities, transport energy for air and water, and energy conversion at the terminal end. Heat Transfer 101 and a touch of Stefan-Boltzmann and that should be a good start. Stick to the facts rather than "opinion" and crunch the numbers first.

Constantin

It's nice to see a number...

... of my former day-to-day colleagues in print.

S Ebels

One has only to look..........

What kind of systems do they use in places/countries where efficiency is highly valued? IE: Most of Europe.

Hydronic

It's just common sense.

End of discussion

Mark Adams

Efficiency and vague calcs

I have been studying this exact subject as I am building a new ranch with a basement and the digging starts next month. I've been comparing gas equipment. First, a gas boiler with 83% AFUE and indirect DHW. Second, a variable speed ECM and two stage 92% gas furnace. I'll assume either install to be top notch and my load calc on the money (with one minor rub).

Ahh, the furnace requires me to install a DHW heater and the best I can find in a tank type with the performance I need has an EF=0.62.

So, let's asssume the total system efficiency for the boiler is 83%. The total system efficiency for the FHA and DHW is (assuming 30% of gas use is for hot water and 70% is for heat):

0.92*0.7 + 0.62*0.3 = 0.83 or 83% equivalent efficiency.

Now, there is a lot of duct loss to the unheated basement, but that loss is serves to heat the floor which in turn decreases the loss from the first floor to the basement. Add to all this the inability of current software to determine the point of equalibrium between basement loss and first floor loss, which would tell us just how much heat to put into the basement to minimize overall structure loss, and we have ourselves an unsolved differential equation and a serious head scratcher.

I think the real answer to the question at hand may have different answers depending on the climate, structure, heat loss, etc.

As for me, I still cannot decide whether to tell my HVAC contractor to put in the hyronic plus ac or just the Cadillac FHA/AC system.

Maybe someone can rustle up a dozen grad students and a local Habitat organization and do a kick a%% study. Hmm, I work at a major University **and** know some folks at Habitat.

Best regards,
Mark Adams
Clarence, NY

rb_6

Ok Constantin

Its time to fess up...if you worked with this crew...what else did you do?

Larry_10

I do not see this as an adversairal relationship at all...

instead i see space conditioning and IAQ or EAQ as a synergy. sorry to say the immediate costs of various onesided attempts have basically proven that the laws of physics remain the same for all of us on this planet. so i am mistaken, big deal...take it up with Ouspensky. as near as i am able to determine the one thing life needs to flourish,as we know it ,is water. so for now , my vote is that water is the easiest fluid to control for the conditioning of our space for comfort.And the other peculiar necessity is for an item we call Air,so,Environmental air of sufficient quantity and quality is what i prefer to breathe. *`/:) keep the faith :)oh i also like sufficent sunlight from time to time so maybe i like the idea of windows also :)Larry ?Larry who?

Kal Row

the answer stares you in the face...

just like the creator of the univers does!!!

and the creator covers this planet with 4/5ths water and cooks it with a nuke

why - "fusion powered hydronics" - thats the ticket...

see - there, that wasen't so hard, was it?

Constantin

A number of things...

... with these guys, I helped set energy efficiency standards (water heaters, washing machines, residential AC/HPs), explore the potential of new technologies in areas like micro-turbines, recycling plants, PVs, SOFCs, etc. In these capacities, my training and experience as an economist and manufacturing engineer were very helpful. I also did some process improvement work in manufacturing facilities across the US.

When I left ADL, I had developed lots of Excel spreadsheets to simulate a business from the bottom up (activities-based cost modeling, to be exact). Tiax is what is left over from the Technology side of ADL when ADL went bankrupt in 2002. Given my super-high billability, some people joke that the bankruptcy was due to my absence in B-school.

However, I stood on the shoulders of giants at ADL, with wonderful resources at my disposal to answer deep technical questions, experience, etc. Without the Guidance of Bill, Detlef, and others, some of my projects would not have turned out nearly as neatly as they did. This was the power of the old culture at ADL, fostering fantastic collaboration, mentoring, and respect for each others work. Sometimes, I wistfully think of my old days when I was a specialist working across many industries...

As my work was not group (but rather project) -specific, I had the pleasure of working with a lot of people within the organization to estimate costs... With the help of Excel and Crystal Ball, you really can put a realistic boundary around business issues, and my models typically managed to be accurate to within 5-10% of actual results. Plus, the output helps you focus on the areas of uncertainty that will have the biggest impact on the business.

People like Jim Bakke of Sub Zero made some big bets on their business based in part on the results of my work. I also helped design and build their Wolf manufacturing facility in Madison, WI. I am very proud of that work, because it proves that American businesses can and do compete globally if they desire to do so, without the need to outsource their operations.

Anyway, in the meantime, I've been to business school (INSEAD/Wharton) and now work as a Practice Leader for intellectual property management for a medical device consultancy. Cheers!

Mark Adams

European hot water...

...is a topic I've longed to discuss with an expert from, well , EU. If culture and tradition are any indication, then I suspect that the EU crowd initially gravitated to hot water because it was easier to fit into multi-hundred year old buildings. Add decades of experience with this and no compunction for A/C, and presto, a continent of hot water heat.

But here in the decedent US, we tear down the old, build the new on the cheap and demand AC, hence lots of cold and hot air.

Just my theory.

All the best,
Mark
Clarence, NY

hr

y'all need to

get on over to www.healthyheating.com and buy the e-book "Homeowners Guide to Indoor Comfort Quality"

There is more, much more, to comfort than just hydronicaly warmed floor surfaces. Send your clients over for a copy also.

hot rod

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Constantin

I agree...

... it is ture that the EU gravitates towards hot water or ductless systems because of the stone walls they typically face in construction. Tearing through multiple layers of rebar is simply no fun, no matter where you come from.

I once lived in a house that had gone through the whole evolution of heating systems... every room had a fireplace from way-back-when. Then, they converted to coal heat and installed an immense coal-fired beast in the basement (7' cube), along with two bunkers. The bunkers and the boiler were then converted to oil. Sometime within the last 20 years, two 2.5x1.5x0.75' gas fired boxes replaced the monster lurking below.

Some older houses in the EU were/are heated with steam heat. Many houses in major cities are heated from central plants rather than having their own heat-generating capacity.

Air conditioning is a more recent phenomenom in the EU because the climate is quite mild due to the gulf stream. The summers are cooler, the winters warmer. Thus, until the advent of office buildings with way too much glass, AC wasn't really needed except for one or two weeks during the year. Now, more people are longing for the comfort they experience in the office at home also.

Interestingly, the advent of ceiling-based radiant heating and cooling is now receiving a lot of interest over there because its more efficient and space-saving at the same time.

In the US, it's relatively inexpensive to install AC ducts because of the construction techniques we use and because interior building space is not valued as highly as it is in the EU. So what if you have to give up 5-10% of the interior volume, we're building a 50,000 sq ft monster house, right? In the urban areas of the EU, Asia, etc. real estate is far more precious than the house that stands on it, and maximizing interior space is priortized accordingly.

For example, if you recall some pictures I posted recently, I showed a Wolf wall-hung boiler in an "attic" space. It is mounted right under the roof (

rb_6

That's exactly why

we wrote the book. Efficiency - comfort – health – all related. Thanks for the comments.

By the way Hot Rod et al, do you remember Lloyd Hamilton that used to drop by, I believe that it is his son, Sephir D. Hamilton that worked on the DOE report…maybe Constantin can confirm.


Mark, here's a table showing savings from the DOE report...have to be careful though the numbers don't always tell the whole story...

hr

I remember an article about that team

in some trade 'zine. was it JLC, Fine Homebuilding, or something??

I commented about it at the Progressive Mechinical site, at the time. Quite a unique project as I recall.

Both Hamiltons, a smart team, use to hang at Area51 HVAC before infighting brought the area to a close

hot rod

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hr

I remember an article about that team

in some trade 'zine. was it JLC, Fine Homebuilding, or something??

I commented about it at the Progressive Mechinical site, at the time. Quite a unique project as I recall.

Both Hamiltons, a smart team, use to hang at Area51 HVAC before infighting brought the area to a close

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Kal Row

did you run the numbers for geothermal liquid heat pumps?..

with solar boost for heating and pool boost for cooling?

did you run the numbers, with low airflow compressor dehumidification as opposed to desiccant dehumidification

for the forced air part - did you use electronic drive variable speed air handlers?

we want answers to all of that – I just hate to buy books on cutting edge stuff as books get obsolete real fast these days – maybe put up a download subscription service

RB_7

Running the numbers

The DOE report originally looked at over 175 ways to reduce energy...if you Click here you can page down to see the ones they looked at in detail. Plus information as to where to obtain the full 281 page report in all its glory. Will make the best of technowienee's blush.

Weezbo

I have visited your site *~/:)

and i find the presentation of material and openness of disscussion to be relevant to our century I would say that in many thoughts the site presents the material in a straightforward logical and coherent way, and these thoughts are basically in keeping with the general thrust of thought embrased in even colder harsher environments further to the north The land of Urasia from what i have been reading on sites from northern Siberia to Great Britain have perhaps taken an even larger Approach to the many variables involved....Japan Korea and Usa have also very advanced studies and reasearch on going along similar lines....the topics of study are being divided up to insure cross referencing and independent accuracy and also bring regional differentiation into the mix....*~/:)

RB_7

If I remember correctly, the Korean word for radiant heating is

ONDONG...now say that without smiling.
[;@)

Bob Morrison_3

It's all in the details of each approach (Bob M)

A benefit of heating water (hydronic) versus heating air, is the ability to use lower supply temperatures with larger surface area emitters, such as with "radiant" floor heating. Lower supply temperatures imply fewer standby losses from equipment (boiler, pumps, etc), which implies a more efficient system: more of the fuel is delivered to the emitter than with a high temperature system. Also, low temperature heat sources such as solar or heat recovery can be utilized. I'm guessing that those notions support the supposed higher system efficiency selling pint than air side systems. But, well designed air systems with high efficiency condensing furnaces are very efficient. I wouldn't be comfortable saying that one approach is more efficient than another. It's all in the details of each.