Question on a complex EK Resolute domestic hot water situation

DonH

Our 3300 square foot house is really a 2100 square foot colonial with a 1200 square foot in-law apartment attached. The in-law apartment has a separate basement that shares a concrete wall with the original house although the apartment itself is continuous with the original house above the basement. Each 'side' has a separate oil hydronic heating system.
We are intending to replace both boilers with a single EK Resolute boiler to heat the entire house.
The new boiler will be located in the in-law basement and will be direct vent. It will pick up the three heating zones for the apartment and there will be a long insulated delivery/return pair to pick up the three heating zones in the main house.
My question has to do with the hot water supply. Currently the in-law apartment has an indirect tank heated by the boiler in that basement. The main house has an insufficient tankless coil in the older boiler there.
We want to keep the existing indirect tank for the in-law apartment but put in a second indirect tank to supply the original house.
The second indirect tank will be located in the basement of the original house where the old boiler was. This is also the location where the heating zones in the original house will be tied into the supply/return legs from the new boiler in the in-law apartment.
The shortest path between the new boiler and the indirect tank in the original house is about 60 feet.
What is the best configuration for supplying heat to each indirect from a Resolute boiler?
Would it be better to buy a new EK indirect water tank, position that next to the new boiler and move the other tank to the original house?
Would a plate heat exchange be needed for one or both of the old and new hot water tanks?
We currently have competing quotes in the works yet neither company could answer this question except to say they think that a plated heat exchanger is optional.

STEVEusaPA

I would wait for the EK gang to chime in. But off the top of my head, I'd do the EK resolute for the in-law side, no indirect.
An another EK for the main house, use the indirect there.
-Or-
Maybe an EK2 for the entire house with indirects closer to the points of use, with/without domestic recirculation
The obvious problem is running a faucet and waiting for hot water. Long pipe runs, even insulated, give off their heat, especially when idle.

HVACNUT

If domestic hot water needs warrant it, you could use a larger EK water heater with a larger plate heat exchanger, and of possible, install a recirculating line. 
Your EK dealer will have options once he or she is on site.

EBEBRATT-Ed

@DonH

I think you plan is sound. I am sure EK will chime in as @STEVEusaPA mentioned.

If you are sure the second apartment will never be rented then I would go with 1 boiler.

As far as the DHW piping I don't thik it will make much difference in the long run. You going to have to pipe heating water back to the larger house anyhow

But

I would lean in the direction of keeping all the DHW indirects by the boiler and run domestic water out and a return line back.

If you put an indirect out in the big house you will be pumping boiler water out and back year round to supply the DHW.

If the DHW comes from the boiler area you will have smaller pipe at lower temp going back and forth during the summer, but in the winter 4 pipes running back and forth

But in the long run I don't think it will matter.

Let's see what EK says

szwedj

Roger is currently out at a show but he will probably chime in at some point.

Personally, I like the idea of keeping the tank(s) on the same side as the boiler too. Now assuming the existing indirect is a 40 gal tank, I would think about upgrading to a single 80 gal storage tank that would be shared for both sides instead of running two separate hot water zones and if possible, consider locating that tank as centrally as possible.

If moving that tank more centrally is not possible, then as others have mentioned, I would consider running a return for a recirculation loop from the domestic hot water supply in the main house.

Your contractors can always call their Energy Kinetics Territory Manager or Tech Support for recommendations on equipment sizing and installation.

Robert_25

The plate HX & storage tank arrangement of the EK is an important design feature, and one of the reasons that the whole system performs as well as it does.  I would go over your expected water usage pattern with your installer and have them calculate what size tank you need.  The long piping run will not be a problem if it is well insulated, and you use a recirc system.

Something else to keep in mind is the basement of the main house will probably be pretty chilly without that cast iron boiler down there.  If you don't have a zone in that basement I would add one as part of the project.

Roger

Thank you for your question, @DonH , and for everyone’s well considered comments and posts.

As it sounds like the heating portion is not at issue, we really want to focus on a good solution to serve both parts of the connected homes. From your description, it sounds like there is significant distance between all the fixtures in the home(s). 

First, sizing the hot water system properly is important as the tankless currently in use is inadequate. When that tank size is defined, and if one tank can serve both loads adequately (which I assume it will be able to), then it becomes in hot water distribution issue; enough hot water needs to be available at fixtures within your (@DonH) expectations for wait time and budget. 

It will cost a bit more to put in a recirculation loop, although that will deliver the hot water quickly for a very good comfort solution. There are other solutions, like the Taco SmartPlus-e system that uses existing hot water cold piping as a return combined with controls to limit operating time to when hot water is needed.

Please post if you have other thoughts or considerations we’re missing. 

Best,
Roger 

DonH

Thank you all for your very helpful comments.
>> Something else to keep in mind is the basement of the main house will probably be pretty chilly without that cast iron boiler down there. If you don't have a zone in that basement I would add one as part of the project.
Robert, I did wonder about that, in fact there is an air register above the boiler room in the main house to vent heat up to the living space. Since the Resolute is a low-mass boiler would I also need to add a heating zone for the apartment basement as well? It's a big space, 1200 sqft., so I would guess that I would need to.
>> Please post if you have other thoughts or considerations we’re missing.
Roger, your assessment of the situation is correct and I appreciate your endorsement of a single tank solution. The only other question is with regard to water quality as it affects the life of the boiler. We have an iron removal system that uses chlorine but we don't have a lot of calcium or magnesium in the treated water. Is there any benefit to using a de-ionizing filter on the boiler internal feed-water line or using de-ionized water in the initial boiler fill?

Roger

Thank you for following up, @DonH .
If you have a basement zone that is not intentionally heated now, your heating pro can do a heat loss calculation to see what radiation is required to adequately heat the space.
Regarding the boiler fill, remember that this is a closed system.  Mineral buildup related issues primarily have to do with leaks in the system. If make up water occurs regularly, it brings in any minerals in the water along with it.  It’s always a good practice to clean and flush the system, although if extensive amounts of minerals are left over in the system from years of prior leaks, it is especially important. If there’s a leak in the system, it should be repaired.
Filling the system with good clean water and using the 8-Way Boiler Treatment included with the boiler is important; using deionized water is not a common practice. 

Roger