Combi System Animations

Comment

Comment by Bob Blanchette on December 10, 2012 at 5:59pm

The combi systems work very well when the heating load is small. Perfect for those situations when you have heating loads under 30k. A conventional water heater can be used with a fan coil. Once you start buying special high BTU water heaters the combi system stops making economic sense.

Comment by Ben Schoenbauer on December 10, 2012 at 12:27pm

There have been issues with the reliability of these systems in the past.  Manufacturers have been working to improve these models and reliability has improved.  There are many manufacturers (Rinnai, AO Smith, American, HTP, Navien, and others) that develop products for this specific purpose and some of them do sell full systems.  

We got interested and involved in this project to support a weatherization project looking to install forced air combi systems as a solution to their need for high efficiency heating with combustion safety and low up front costs. It did take a large effort to optimize and install these systems. We are currently developing best practices and optimization guidelines. Going forward we are looking at several ways to improve the system by reducing the need for optimization and making these systems more accessible to everyone.

   

Comment by Lester Shen on December 10, 2012 at 11:48am

Thanks, Jon. That is indeed a typo. It should be CFM. We'll get that amended. 

Comment by Jonathan Beers on December 10, 2012 at 11:37am

In the final animation, what's "CPM" stand for? Possible typo for CFM? Back when the Lennox Complete Heat and the early Polaris systems were on the market, a few contractors I talked to reported bad experiences. I heard that the more recent attempts at these systems using Munchkin boilers also had some problems.

Building Science Corp put out this document several years ago:

http://www.buildingscience.com/documents/reports/rr-0213-combo-spac...

Comment by Robert C. O'Brien on December 10, 2012 at 11:14am

In the northeast,where the majority of residential boilers are,these are referred to as hydro air systems,a combi is heat and DHW in one unit with heat delivered not using air as a transfer medium ie conventional radiation

Comment by Greg La Vardera on December 10, 2012 at 11:00am

Wait - the description in the above post says "dual integrated appliances". But everybody is talking about cobbing together systems that were not manufactured for that purpose. 

Nobody has an example of a US manufacturer offering an integrated appliance?

No offense intended, but is it my imagination that Energy Consulants are really not interested in dual integrated appliances because many earn a living advising people how to cobble together this kind of system?

Comment by Pat Dundon on December 10, 2012 at 10:47am

My best experience is with a boiler and indirect water heater in a baseboard hot water house.  I found a good way to improve it is a solar hot water system between the well and the indirect tank with circualtion between the two on a relay.  In summer it doesn't overheat, it just makes 120 gallons of 140 degree water.  in my cloudy cold winter environment it means the indirect unit is usually heating water from 75 degrees or hotter to 120, instead of well temperature. 

What I don't know about is wall hung gas fired boilers with built in indirect water heaters. Apparently Rennai (sp?) is building a unit with a 6.5 gallon onboard water heater and instant on hot water combined with a space heating boiler.  I don't see that illustrated here.  does anyone know if they are really effieient, and if so, does the family size effect efficiency because the water runs more? 

Comment by Ben Schoenbauer on December 10, 2012 at 9:50am

Great to see all the interest in this topic.  As Lester mentioned we are currently conducting a field research project (funded by Building America) to characterize the potential of these systems.  Forced air combination systems have been around for a while, but have recently started to be considered again.  There are many manufacturers that offer system components.  Most major water heater manufacturers offer a water heater designed to be the heating plant in a forced air combi system.  Several (including Rheem and Rinnai) have full systems with both the air handler and the heating plant.  

Preliminary results have confirmed the high efficiency potential of these systems. By carefully sizing system components we have been able to reduce water temps and install systems with 90% space heating efficiency.  Performance varies depending on installation, usage and the type of water heater, but our optimized systems have energy use comparable to a condensing furnace and a condensing water heater and because you only need to install a single condensing heating plant installation costs can be reduced.

Comment by tedkidd on December 10, 2012 at 7:23am

Fantastic early Dan Holohan boiler article http://bit.ly/danholohan1992allshookup

Building Science Theory :: a great overview from Bean http://bit.ly/HHhpOverview

BSC Experts Session - Straub and BTU http://bit.ly/BSCexpertsSTRAUB

Comment by tedkidd on December 10, 2012 at 7:18am

These systems definitely have their place, so long as designers understand the unavoidable efficiency sacrifice due to inability to run low water temperatures.

Conflict occurs at the water to air coil. To have effective transfer here, the water must be hot. Dan Holohan, Robert Bean, and as of last week John Straube of BSC have all published the power of running water in the 80f range, a temperature not possible when you add another heat exchange distribution step.

Ideally distribution is directly connected to combustion. This allows lowest possible temperatures, which in turn pull/wring/squeeze (imaging squeezing a sponge) the most BTU out of both the sensible and the LATENT heat of combustion.

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