System design advice for new home with panel radiators

aroshtr

Hello my name is Joel. This is my first post on the wall, but have been following and learning for a while now. The information on here and the knowledge of the members is amazing. Thanks to all who contribute.

I will be building a new home soon, and have been planning my hydronic system, and was hoping for advice so I don't make too many mistakes. I am a diy'er and will be installing the hvac system mostly myself with some assistance from my plumbing contractor. I am trying to come up with a system that is efficient, cost effective, and not overly complex for me to design/install/program.

The home is one story with a full basement, 1236sf per level. It will be well insulated, shooting for 1.5ach for tightness, and have triple pane windows. I have done a couple of room by room heat loss calculations using online calculators. They came up with approximately 30-31k btu heat loss for the whole home. We are located in zone 6B in Great Falls, MT. I have natural gas, and plan on using a hot water heater (HTP Pheonix LD 60g, or westinghouse equivalent) for both domestic and the closed loop heating system. I will be using 10 panel radiators and one towel warmer that are controlled by TRV's. There will be a couple short runs of staple up floor heat for floor warming in the kitchen and master bath. These short runs I planned on using the exiting water from a radiator/towel warmer on its way back to the manifold (water temps could be close to 120 on design day, and not sure if this is a bad idea for staple up with aluminum plates). I will be using an 11 port stainless manifold with home runs to each radiator. I am sizing my radiators based on a supply water temp of 140 on the design day temp.

Option 1: I picked up a Taco x-pump block (xpb-1) for a good price, and like this setup for simplicity. However there are a couple of issues that have me second guessing my decision. This is a Delta t variable speed pump, and a lot of sources say a Delta P pump is a better option for TRV's. I also realized that these are not ECM motors, and over time it will likely cost me more than if I designed a system with ecm pumps. From reading the instructions, I would like to use it in outdoor reset mode. It requires a "demand signal" to activate the circ pump, and I originally didn't want to have a thermostat in the home and rely on the trv's only. It looks like I will now need a thermostat in the house somewhere. I am just not sure where to place it and what to set it for? Would it be possible to use two thermostats, one on the main level and one in the basement wired to the same pins? I am guessing a T-stat in this situation would simply be an upper limit. If at least one of the thermostats was calling for heat, it should close the circuit. If both levels were at or above set temp it would shut the system off. Would this work? The other option would be to simply have an on/off switch in the mechanical room to shut the heat system off. I just worry if the system is turned on and no TRV is allowing flow, what would happen. Would the pump burn up?

Option 2: Use a variable speed Delta P pump like a Alpha 2 or Viridain on the heating loop side. This would have to be supplied through a BPHX and another pump on the water heater side. Would this pump need to be variable speed, or constant speed? I am just totally lost on how to control the pumps in this setup. Not sure how the water heater pump would be activated when the heating loop side is pumping. Not sure if I would need a thermostat to activate the pumps, and how outdoor reset would be programmed into the system. I guess my lack of knowledge is why I really liked the simplicity of option 1. If I go this route, I will likely need assistance from a pro.

With either of these systems, will I have to run my water heater at 150 or 160 in order to get the supply water to the radiators at 140 on design day? I just don't know the efficiency of the BPHX. Is it possible to also run the water heater on outdoor rest independent of the heat pumps?

I know this is putting a lot out there, but know you guys can give better advice with a clear picture of what the total system will look like. I will appreciate any advice on any aspect of my design. THANKS!

Jamie Hall

Please do yourself a huge favour and do NOT use a water heater for your heating system. It's fine for domestic hot water. That's what it was designed for. It's NOT fine for heating. It was never meant for that. Efficiency is poor (relatively speaking) and it was never intended for continuous operation.

Now.

Since you have natural gas, and a rather small heating load on the design day, your best option -- it will cost a little more to begin with, but will save energy -- is a small mod/con gas boiler for the heating system. There are a number of good makes out there.

aroshtr

Thanks Jamie, I originally considered a mod con, and it is still an option. However the cost kept increasing as I would also likely need a decent sized buffer tank to deal with short cycling of the low load and trv's. If I went this route, I suppose an indirect water heater would be a good choice too. It is probably a few thousand more to go this route, but I will consider.
Side note: My wife and I are empty nesters, and have fairly low hot water needs. Also we will be mostly living on the main level, with the basement as bonus and guest use. So it will likely be ran at a lower temperature like 62 deg during a most of the heating season. So the actual heat usage of the home is likely closer to 24k btu/hr at design conditions.

Hot_water_fan

I think a modcon would suit you better - with an 8k Btu minimum fire, you could get an 18 gallon buffer tank and eliminate short cycling. Your flow rates and head loss with 11 radiators and 30k BTU heat loss will be very, very low. Nice! The smallest pump you can find will probably work for the system side, probably 3,000 BTU/W for pumping efficiency. One question - why not bump up the panel sizes a bit? Either 11 slightly larger panels, or combine some smaller ones into larger ones (unless you have 11 rooms of course). You could run lower temperatures and buy fewer TRVs, a smaller manifold, and less tubing. Could save you both upfront and over time. 

mattmia2

There is a high mass boiler version of the phoenix that could be used with a hx or an indirect to make dhw.

Among numerous other issues, trying to use a water heater for domestic heating, especially with the size of your system, you would have to run it hot enough to disinfect the water and you still would have water quality issues.

I would strongly suggest you get a copy of Modern Hydronic Heating and read it.

If you want to use radiant, you should really separate it out with separate zone controls and mixing to make low temp water.

the transfer rate of a hx is related to the surface area of the hx and the temp difference, so you can get a closer approach temp between the 2 sides by using a larger (and more expensive) hx.

aroshtr

H_W_F, I might try to enlarge the radiators slightly more, and see if I could use lower temp water. As far as combining circuits, it might be difficult. Most are separate rooms that may be at different temps. In my main living area, I had a separate zone for the living room, and dining area/kitchen. It is open concept, and I just might be able to combine these into a series loop.

Mattmia, My proposed system is not an "open" system. It would be closed and fully separated from the DHW side. So there should be no reason that I would have to run it hot enough to disinfect, and I don't know why there would be water quality issues. I could be missing something, but wanted to clarify.

Thanks for the ideas, and help. I still am nervous about designing a system that to too complex for me to assemble and run, and want to keep costs as low as possible. That is was why I moved towards the high efficiency water heater in the first place. I originally liked the idea of an all in one device like the HTP Versa Hydro. However it seems like overkill, and is fairly expensive.

Hot_water_fan

Looking at this closer, water heating might not be the best fit for this house if you're concerned about cost. You've described a well-insulated, air-sealed home with a very low heat load. If Great Falls has 8000 Heating degree days/year, with a heat loss of 30k Btu you're only looking at ~65MMBtu/year. One of the strengths of hydronics is it's ability to scale, but the flip side of that is that 11 small radiators (say 3k Btu each) and 11 TRVs don't cost much less than 11 large radiators. Add in a buffer tank, manifold, circulator, expansion tank, strainers, tubing, etc. you're looking at a huge bill in materials alone before even getting to the boiler itself or the expertise required to do this safely. I'd take a look at some alternate options. Using NorthWestern energy's rates (low cost hydropower) and low cost natural gas, the mod con is cheapest to operate, but only by $50/year compared to a cold climate heat pump (centrally ducted). One option that might be uniquely suited to your home and plans for the basement would be getting a ductless minisplit for the largest room or two (what Mitsubishi calls a floor mounted minisplit looks the same as a panel radiator). It would be both highly efficient and cheap to install. Combine that with some electric baseboard in the smaller and infrequently used rooms, and you'd get the room by room control you'd have with the TRVs, but since the minisplit would handle half or more of the heat load, the efficiency of a centrally ducted heat pump. In addition, it would provide lots of redundancy - if any baseboard failed, you'd still have many others. Lots of contractors can install these baseboards (you could contribute too) and they have long, maintenance free lifespans. That would be a balance between control and zones, but you'd give up some efficiency versus a ducted heat pump that serves every zone. A ducted heat pump would have resistance backup, so you'd have at least one backup. That would likely be the cheapest to install and operate espeically if you take modcon maintenance into account, but it wouldn't provide zoning.

mattmia2

Where is the heat exchanger to the dhw that makes it a closed system?

aroshtr

Matt: If I use the Taco xpb-1 x-pump block, it is integral to the unit. If I were to go option 2, then I would install one in between the water heater loop/pump, and the radiant heat side/pump. Sorry I did not make that clear. I definitely would never do an open loop system with all I have learned so far.

H_W_F: I realize there is probably more economical options that I should consider. A cold climate whole house heat pump system is probably the best and simplest solution that also gives us AC. There will be a gas fireplace in the living room as well. We use one currently for room comfort and aesthetics. But It might be necessary on really cold days if the main source was an air source heat pump. However, what my wife does not really want, is another traditional forced air system. We were really looking forward to the comfort of a radiant heat system, and would like to do that on the most economical basis. Your idea of using EBB in the rarely used rooms in the basement (storage room, & guest bedroom) are a good idea. The storage room which has no windows, and is 100% below grade, will probably get adequate heat from adjacent walls to the family room and mechanical room. That would eliminate 2 radiators, TRV's and Pex.

Hot_water_fan

Understood! No problem with that, just wanted to make sure 4 to 5 extra figures is worth it. Related to the comfort part: you can probably skip the radiant floors. Maybe try an electric radiant floor in the bathroom? In the kitchen, if you’re running maybe 12 btu/sqft at design day, unlikely you’ll ever notice any heat. The floor will be barely, and I mean barely, above room temp. 

Jamie Hall

All good thoughts up there. But I will add a comment: you mention that you are trying for 1.5 air changes per hour. That is actually below what is a desirable minimum, in my opinion, to maintain indoor air quality. I would advise not going less than two air changes per hour. At some risk of sounding like a fanatic -- which I am not -- unless everything inside the house is "natural" (finishes, fabrics, insulation, building materials, furniture, you name it)-- which is almost impossible to achieve in a modern house -- and there are no fuel burning appliances or oddments -- even candles -- you want some air exchange.

Now... if you are concerned about energy efficiency at the same time, there is much to be said for sensible heat recovery ventilating systems, as they recover as much as 70% or so in the air exchange and they can be built into a very tight structure to control that air exchange.

aroshtr

Jamie, Good point. I will be installing a Panasonic ERV with dedicated duct work. The erv will be balanced, but I do not think I will install any makeup air system for the range hood or dryer. So there will be some negative pressure in the house while those are running.

Jamie Hall

If at all possible you should arrange your boiler and water heater so that they have independent outside air available for combustion. Otherwise the negative pressure which you mention (and range hoods are really good at that!) will disturb the burner adjustments -- and in extreme cases can cause problems with combustion exhaust getting into the house instead of going where it should.

Zman

If you have a limited budget and you can live with the short life span of the hot water used for heating, option 1 would work well. Your deadheading pump concern is real, fortunately, this would solve your problem. https://www.supplyhouse.com/Bell-Gossett-113247-3-4-Differential-Bypass-Valve?gclid=Cj0KCQjwna2FBhDPARIsACAEc_U90my281Js1Xrv6qODcu5QzY2T542XlCeuVBFzNw9JEnQS-O0xBdYaAlejEALw_wcB

hot_rod

ECR, Utica Boiler offers a nice heat exchanger package the could be used with a high efficiency tank type water heater. That might get you the high efficiency you want, safe isolation, a buffer, and the ability to size the circulator appropriately.

aroshtr

Zman: Thanks for the bypass suggestion. I will crunch some final numbers, but it should be be significantly less up front costs to go with the water heater instead of a boiler/indirect/buffer tank option. I will try to do some estimates on longevity and replacement costs as well. Also mechanical room space might be an issue too, and a single water heater would definitely take up less space.

Bob: Thanks for the suggestion on the Utica DHW module. It looks like a nice package. I sent the company an email on where I could purchase, and pricing. Have not hear back yet. There are no dealers anywhere close to my area. If you know of a company I could contact that might sell to a diy'er, let me know. Thanks

For other readers interested, here is a link to the item Bob suggested. https://uticaboilers.com/products/boilers-oil/utica-boilers-domestic-hot-water-module

mattmia2

I think you might be overthinking the buffer tank. I think you may be able to go with the smallest boiler you can find with a 10:1 turndown ratio, especially if it is a fire tube so it has a bit of mass itself, you use some of the short cycle prevention features in the boiler like the minimum off cycle timer and design for a relatively large differential in the supply water temp and you give it a lower max firing rate for dh calls so it doesn't try to get up to the requested swt as fast as possible then shut off on high limit and the mass of the runtal radiators and their water content will take some time to heat and cool.

This does mean you may need to use a relatively large indirect to handle dhw depending on how much you need and your incoming water temp in winter.

Rich_49

Jamie Hall said:

Please do yourself a huge favour and do NOT use a water heater for your heating system. It's fine for domestic hot water. That's what it was designed for. It's NOT fine for heating. It was never meant for that. Efficiency is poor (relatively speaking) and it was never intended for continuous operation.

Now.

Since you have natural gas, and a rather small heating load on the design day, your best option -- it will cost a little more to begin with, but will save energy -- is a small mod/con gas boiler for the heating system. There are a number of good makes out there.

This used to be sage advice . Not so much anymore , especially considering what you describe wanting to build . I have used these in many projects in the coldest climate when it was the right fit . It is efficient as hell and built just like you're thinking with 2 control programs , 1 for heating and the other for DHW . Worth the money , everything warrantied , backed by a reputable company , the same company you are looking to purchase from anyway . You cannot build it as well as they did and you won't save any time or money trying to duplicate it . Times change and so must our thought patterns or we too , like the dinosaurs will be extinct .

https://www.htproducts.com/versahydro.html

Rich_49

Zman said:

If you have a limited budget and you can live with the short life span of the hot water used for heating, option 1 would work well. Your deadheading pump concern is real, fortunately, this would solve your problem. https://www.supplyhouse.com/Bell-Gossett-113247-3-4-Differential-Bypass-Valve?gclid=Cj0KCQjwna2FBhDPARIsACAEc_U90my281Js1Xrv6qODcu5QzY2T542XlCeuVBFzNw9JEnQS-O0xBdYaAlejEALw_wcB

Constant circulation is a good idea when using Panel rads and TRVs . Deadheading will not be an issue if you use Bypass H valves at the radiators . Very easy when all is considered . Can give you contact information for several people using the VersaHydro with panel rads , radiant floors that have experienced nothing but good stuff and lower fuel bills .

Feel free to call me , talk is free .

aroshtr

Richard, I have looked at the versa, and really like it. The high 130,000/100,000btu heat rating sorta had me worried it would be oversized. The price is fairly high, but not out of line after all the components and time involved to basically mirror the system with a HE water heater.

Not sure I fully understand the lack of deadheading issue "as long as I use H valves". I originally planned on a direct home run to each radiator, with direct connection with no H style valves. I would adjust flow as needed at the manifold. One solution I thought of would be to use an empty port from the manifold with a short jumper between outging and incoming sides. I could balance flow way down, or add a add a pressure bypass valve on that short loop. If I did use H valves, would I need one on every radiator? Or could I just add one somewhere in the system to allow some minimal flow?

I really value your input, and know you have a lot of experience with systems similar to what I have planned. I actually contacted you by facebook a while ago, and you gave me some good starting points and direction. I should probably just hire you to spec my system, and avoid a diy design mess.

Rich_49

1 could certainly work . I usually use several , that way heated water is right there at every rad ready to get to work . They are not much more than a non H valve after all .

Far as the Versa goes , when all is considered , it is not that expensive . Don't be concerned with the 130,000 rating , with 55 or 80 gallons of mass and the programming options short cycling is not a concern , the low end is 35 K .

Please do not use a differential bypass valve , EVER . It is a band aid for a self inflicted gun shot wound . With the choices of VS ecm circs available now there is never a need for one except on existing systems if even then .