Looking for small combi boiler / AC unit

Matt_Connolly

Hello,

It's been years since I've been on this board. I used to be a rep for Monitor boilers. I'm renovating a 6 unit apt. building and looking to use combi boiler for domestic hw and fan coil in the A/C air handler. I'd like your input on the best way to skin this. There is space so a big Triangle type would work. Heat load is about 30,000 per unit. a/c load one ton max.

Thanks,

Matt



P.S. I hope all the great guys I met in the industry are still out there!

SWEI

loads

Am I correct in reading that the total space heat load is180K at design conditions?



Have you done a DHW load calc?



Where is this project located?  Design temps?  Is this a new install?  If not, what is being replaced?

heatpro02920

I'm confused, but that doesn't take much...

Do you need the boiler, air handlers, outdoor units, ect?

Are they looking for maximum efficiency or just cost effective enough to get rebates?

I take it the utilities are shared so one central system for all 6 units is the idea?



If you need everything, not seeing the building and not knowing the budget, Im thinking...



6- 18 hbxb-HW air handlers

6- 4shp16lt heat pumps

2- TT solo 110 boilers {6 bumble bee pumps, 0011 primary}

1-6zone taco switching relay}

2-Rinnai ru98i tankless units



The heat pumps will cool and heat down to your set temp, then the boiler will kick in when it gets to cold for the HPs, I would go with 2- 110's so you can mod down to 30K and then ramp up to 220 when needed {thats input, your max output would be around 180K BTU} so when one of the 6 air handlers calls for its 38K btus you will be in that area {hope I worded that rite for you}... The building owner should get rebates for the tanklesses, the heat pumps, the 16 seer, the boiler, and be happy... Since the heat pumps are going to work down to the 40's you don't have to worry about short cycling becaus the boilers are only going to call on the sub 40* days, and since the trimax control will handle the cascading for you no external controls are needed, except the zone control of course.. I would wire the bumble bees for delta t operation and try to keep it around 25* which should be easy...



I did almost this identical system, except they did 3 rinnai units because it was 3 floors, but it was 6- 1.5ton hbxb units, with 6-16 seer heatpumps and buderus boilers before I started using the TT's... I also installed a HWC1520 on each air handler I could run much lower temps {but the heatloss was around 40Kbtu for each unit in my job}...



It worked very well, the heat pumps are great for the 50 degree days when you just need a little heat, I use a similar system in my own home, my boilers only run 3-4 months a year... as soon as 43 degrees rolls around the boiler kicks off and the heatpumps are kicked into action, and I use a tankless for dhw.... I am a firm believer in only running the boiler when it is absolutely necessary, most heat pumps are more efficient down to around 40*s, the equipment lasts longer, spreading the load over multiple stages keeps everything in service for a very long time...



If they want it even more efficient, run the hwc1520 coils with the air handlers, this will allow you to easily run 130* supply temps.... the case coils are inexpensive, and if you do it rite you wont even need to make a transition for the dw, just come off the top with a duct connector.... first coil pipes in last {again hope that makes sense, you want the first supply to run into the case coil and that return to run into the air handlers coil then return back to the primary loop. Keep an eye on your head psi, but if you use 1" pex you wont have any issues.... You can also go with variable speed units but they cost much more than the hbxb units and I never did the install this way withthem, I fear they will HUNT if the variable speed control is working with the ODR changing the temps, and the delta t circ changing the flow, this may cause a wrinkle in the space time continueum and kill us all....



One more note if you go with rinnai units, I would grab a 009 stainless circ so you can run a recirc loop, most big buildings will appreciate this, and the new tanklesses have the control built in to handle the 009...



PS- a good way to sell the system is to let the customer know that the heatpumps will supply aux heat if the boiler ever goes down {or in your case both boilers, dont word it that way though, lol} the heatpumps will work down to 14* or so, but they are only really efficient down to the 40 range before it makes more sense to run the boilers, depending on your electrical costs and gas costs...