Design help?!?

Tcatflyer

Hi, wondering if anyone knows of a design service that is reasonably priced where I can give design parameters and desired operation so that I can build it myself. I'm a retired electrical engineer and always have had alot of interest in this stuff. I have an electric boiler, propane boiler and would buy anything else necessary. My floor has been working for the last couple years but I'd like to use the propane boiler for a recirculated dedicated hot water loop. I don't have an issue putting that together but would also like to use that 200k btu/h boiler to heat glycol via a plate heat exchanger for snow melt as well as cycling hot water 180 deg through some radiant base boards to top off the temp during these -30 deg F evenings when the house cools down. There's also a coal boiler getting commissioned this summer that will add approximately 150k btu/hr to my heating needs. It's located in my machine shed and I plan on bringing water underground @ 180 degrees into my house. I suppose there will be a PHE to strip that energy off that glycol.

I get all the pieces but would like help putting it all together.

Thanks in advance!

Darin

mattmia2

With that many systems interacting with each other the devil will be in the details. If you are going to install it you will have to understand how it works. Coordinating how all the pieces interact and how they interact with the actual field conditions will have to be up to the installer. An engineer can tell you that you need this much radiation here or this much tubing in a slab but there will be some parts of how it goes together that will have to be worked out as it is installed. It would be an enormous amount of work to even try to detail all that out. What an engineer can do is show schematically how it all works together and typical details of how things are connected together.

Tcatflyer

This is what I see going on for the most part. Along with these design considerations listed below:

1.System will use coal boiler energy when it's available as a priority. The system will work workout it with a slight compromise in snowmelt performance.

2.T101 will be at 180 deg when coal boiler is in operation. Roughly 140 (due to PHE 2) when coal boiler is off. In that event electric boiler will top off temp to 180 deg.

3.Total energy demands for radiator loop is approx 36k BTU/hr. This loop is necessary to maintain even temps in house during the evenings when inside temps drop.

4.Electric boiler will be set on front panel to 180 deg. No further controls are necessary.

5.Pumps 101, 102, 103 and 104 are controlled via individual thermostats. No further controls are necessary.

6.160k BTU/hr propane boiler will be set to 140 deg and will operate pump 201 in "economy mode". No further controls will be necessary.

7.Mag flow meter 201 and temp sensors T201, T202 and T203 are used to track energy distribution via PHE7 and PHE2.

8.200k BTU/hr propane boiler will be set to 140 deg and operate pumps 301 and 601 in "economy mode". No further controls are necessary.

9.Mag flow meter 301 and temp sensors T301, T302 and T303 are used to track energy distribution in PHE5, PHE6 and PHE8.

10.Total energy demands for snowmelt loop is approx 300k BTU/hr.

11.Snowmelt loop will be turned on by energizing pump 401. No further controls are necessary.

12.Total energy demands for house and shop floor loops is approx 80k BTU/hr.

13.The desired water temp going into the house and shop floor loops will be adjusted by the electronic mixing valves via PLC as the temperature trends fluctuate outside. 

I need to size pumps for head and flow as well as plate heat exchangers.

If anyone would like to add some comments they'd be much appreciated.

Thanks, Darin

hot_rod

Your top row of PHE look to be in series, so a temperature drop as you go through each one. The snowmelt HX could really drop the temperature down. You might parallel or RR those?

Why so many HXers throughout the piping? Every HX requires an expansion tank, air and dirt purgers, fill system.

You have some serious calculating to do to size and pump all those HX properly. You need gpm flow rates and temperatures, at least 3 variables for each. Download one of the HX sizer programs. Do an online tutorial to learn the inputs.

The coal boiler will need return protection of some sorts.

Tcatflyer

They are in series because of priority. The first one will only strip a max of 30k btu/hr if it's in full demand (which it most likely never will be during the day when I'm melting the snow outside. The second one is for the snomelt system and it will most likely drain all the energy from the coal boiler easily with a large 60 or 70 plate heat exchanger. The third will get the balance when the snomelt system isn't in operation. And will have perhaps 120k btu/hr when the radiators are demanding heat. The number of PHE are necessary to maintain flexibility in having the coal boiler supply all energy demands but still have the system operational when the coal boiler isn't in operation. I could be wrong on that as there may be an simpler way to accomplish that but I don't think so. That is where I'm looking for help. Looks to me I really need a minimum plate heat exchanger size I can install ones with more plates with only minimal pressure drop increase. Just wasting money on larger plates than necessary. I've hooked up one and have transfered 150k BTU from one stream to the other so I'm close anyways. Really what I'm looking for is someone to say, "hmm, an easier way would be to do XXXX". But again to have this amount of flexibility in where the system can get energy (coal being the priority) it's my experience these heat exchangers are necessary.

Thanks for the comments!

Kaos

I really think this illustrates the beauty of hydronics. There is no limit to the system one can make.

JDHW

Are the propane boilers cast iron or mod/con?

hot_rod

seems like the only place you need a HX is on the snowmelt?

Why can’t the same water be in all the boiler as if they are closed loop piping. You have numerous mixing valves so all loads could be parallel and receive the same temperature.

You have both pressure and temperature drop to account for with the series HXers.

If the first load is running the second snowmelt gets x temperature, so you size the HX for that. If the first load is not running and the snowmelt is, the HX is not sized the same as the SWT determines the HX sizing. The third load is even more complicated to size depending on load 1& 2 being on or off.

if all loads, HX received 180, SWT the HX sizing is pretty straight forward.