When does indirect make sense?

jb9

Hello,

I have a question that is related to radiant + DHW design approach. I am definitely learning a lot as I read as much of the Wall, healthyheating and the Caleffi educational magazine as I can digest. On the forum, I see a lot of folks who are troubleshooting an existing system or a component thereof. In my case, I am still designing the structure, but have a good sense of the square footage (1500), the floors (2 + a basement which will contain my mechanicals) and the bathrooms (2 1/2). As I increase my understanding, I am leaning towards an indirect water heater as I am reading how a boiler can work to support DHW. At first, it seemed like having the two systems separate made sense conceptually, but the more I read, it seems like an indirect water heater system is a good idea. My heat load isn’t going to be huge (SIPs enclosed structure). When does a designer make the decision that the two systems (radiant + DHW) can be integrated (such as with an indirect water heater)? Are the two driving factors the total heat loss (boiler) and the DHW demands (using the fixture count, peak load, number of concurrent users, etc)? And what are the scenarios that might inform a decision to NOT integrate the boiler and the DHW tank? My hope is to use an air to water heat pump or an electric resistance boiler to drive WB.

Also, when I look at the Idronics Issue #11 (DHW), I see how the coil on an indirect system runs into the HW tank and then runs down and back out, but is there also a heat source in this tank as well?

Sorry for the somewhat random questions, you guys all know the acronyms (I found the acronym page a month ago) and I have been trying to fill in the blanks so that I understand how to properly “start a design from square one” rather than troubleshoot a faulty or ill-designed system.

Also, for clarity, I absolutely plan to make sure the hydronic heat will be a "closed" system. I have seen that reiterated many times for obvious health and safety reasons.

Thanks.

hot_rod

If you decide to store DHW in a tank, search for a well insulated vessel. Indirects are great as they have no flue and that greatly limits standby loss. They also leverage the efficiency of the device that drives them.

Another option is instant DHW production via a boiler or heat exchanger or separate tankless type heater.

Determine that building heat load number, then pin down the amount of DHW you need for the family.
Commonly we use 15 gallons per person per day for a DHW number, but it varies like fuel mileage.

Solar preheat and DHW recovery tubes are another option.

Brewbeer

If you are using an all electric space heating source, an electric water heater might be your best option.

Rich_49

What is your location and whose A/W HP are you considering ? These are very important questions for us to offer competent help in your decision process .

jb9

Hi @Rich. The location is southeastern Idaho (I believe climate zone 6). The A/W Heat Pumps that I have been looking at are the Chilltrix and the Daikin (sp?). I am a not a pro, so feel free to suggest other manufacturers that I can research. All the folks here are pros and know the myriad of product offerings out there (and what problems they solve)... It sounds like the limited output of electric boilers may preclude an indirect heater design. I figured I would ask the theoretical design question first and then try to add detail as needed.

Rich_49

Any gases available ? Will you have backup power generation on site ?

Please tell us more about the building and why you chose warmboard ? Did you purchase it yet ?

jb9

Hi Rich,

There is LP available, but I don't want to have a large tank on the lot. Regarding the WB, I am considering the WB-S product and hope to leverage the fact that the labor of the install can be combined with the subfloor. It does seem quite robust. Also, I know you are a fan of Sunboard, but I haven't really been able to get enough support (samples, info, etc.) from the manufacturer. I have been getting a lot of support from WB and I haven't even started my project yet. I am assuming that the recommendation could be informed by the lower supply temps from an 8" OC versus a 12" OC system. Hopefully, a 12" OC system can be powered by a boiler running on electricity. Again, my initial inquiry into the indirect system was coming from a place of trying to understand how designers start a whole house project. (DHW and hydronics together). Hope that clarifies it.