Pleas advise: Cast iron boiler with water source heat pumps

Jason Quinn

I will try to keep this short. I looked at a project today in a rehab facility that consisted of an 800,000 btu steam boiler piped to (2)- 11/2 inch steam to water heat exchanger plates. The "B" or water side of the 2 heat exchangers, also 11/2 inch, supplied water source heat pumps throughout the building thru a common 11/2 header that connected into 4 inch supply and return mains. My first thought is that this is a bottleneck and they are not getting the full output of the boiler or heat exchangers.



I am not that familiar with heat pumps. The contractor that was showing me the job, was recommending to replace the steam boilers with conventional cast iron hot water boilers and pipe direct to the heat pumps. He also added that the water temperatures from the boiler would be around 80- 100 degrees to the heat pumps. I advised him against this as the water temps are too cool and that the flue gases will condense and rot out the boiler.



I considered multiple mod cons, but the venting would be near impossible. So, I have also considered separating the boiler side from the heat pump side by way of a heat exchanger, a 4 way mixing valve or possibly variable speed injection pump; all of which would provide boiler return water protection.



Any suggestions? Should I post this in the heat pump section?

Henry

Mod/con

The contractor has no idea of what he is talking about. It is time to get a professional involved that will  calculate the heat loads and payback on mod/con boilers. We have done several installations recently with Lochinvar Knights and geothermal systems with great success. At friends house. we installed a 23 zone radiant, hot water, garage space heating, pool heating all done by a 6 ton geothermal supplemented by a Knight.



Henry

Mark Eatherton

What Hank said...

I have seen those situations where a conventional appliance was installed. Some with protection (4 and 3 way and VSI) and some without protection, and they ALL looked like hell on the fire side.



Why chance it? Why not put in some thing that is DESIGNED for extreme low temperature operation.



Also, FWIW, I have never seen a water source system that required heating water supply temperatures over 70 degrees F. In fact the few I have worked on used 70 as the set point for heating and cooling. Heat was added if the fluid dropped to 65 degrees F, and heat was rejected if the fluid got above 80 degrees F.



By all means, check with the HP manufacturer, and conform to their requirements if you want to retain any kind of warranty.



ME

Jason Quinn

Thanks for the info.....

The water temps required may be only 70 degrees. Don't know if this makes a difference, but the boilers are the ONLY source of hot water to the heat pumps- they are not supplemental. There is no ground source loop installed.



Mod con is the way to go here. Just have to figure out how to individually vent them. They want DHW to be independent. Perhaps 2 mod cons for the heat pumps and 2 for dhw and utilize the existing 16 inch chimney as a chase for the pvc exhaust vents?



Maybe a silly ?, but is there a mod con available that can be common vented? Thanks again for any insight.

Mark Eatherton

I believe so...

I know for a fact that Munchkins have been commonly vented using a draft inducer (variable speed) that works quite well. You will have to size the boilers to the actual loads attached, and you could use the same boilers for doing DHW production through reverse indirects. Make sure that whatever you do, you run it by the appliance manufacturers engineering department.



The theory of design on water source heat pump is that there are many times that half the building needs heating and the other half needs cooling. The loop essentially allows you to recover the heat being rejected for those areas that need it. There is usually a closed loop cooling tower that is used to reject excess heat.



If all zones are calling for heating, then you are putting heat into the loop. If all zones are calling for cooling, then the cooling tower is on maintaining the loop temperatures. I have seen some hybrid cooling towers to increase cooling, but they only work well in areas of low rH.



ME

Jason Quinn

Chemicals in the water loop as part of preventative maintenance?

I have been doing some research and have read that chemicals are added to the cooling tower and water loop as part of preventative maintenance. If a mod con is piped direct to the water source heat pump and water loop, will these chemicals damage the boilers heat exchanger?

Mark Eatherton

Chemicals....

are a part of hydronic life in commercial settings, and should very well be a part of residential settings as well.



The cooling tower chemicals should NOT be getting into the closed loop portion of the system. If in doubt, get the make up of the chemical soup and run it by the boiler manufacturer. Usually, these chemicals are beneficial to most boilers, but better safe than warranty less...



You also have to watch the operating temperature. I've seen water based heat pump loops in tall buildings that might push you overboard as it pertains to operating pressure if your heat source is on the bottom of the system. If need be, you might have to ad a heat exchanger to keep the boilers from seeing the high pressures required to fill a tall system.



ME

Steamhead

Which may be the reason

the steam boilers and HX units are there. How tall is the building? 

Jason Quinn

Thanks for the help...

The building is 55 ft tall from the boiler in the basement to the roof and cooling tower. The highest heat pump is 40 ft above the boiler. Does the boiler water loop need to go to the cooling tower or are these two loops separate?

The chemical is "One-Tyme" water treatment and condenser cleaner by MFS.



Once again, I appreciate all of your input. I am unfamiliar with this type of system; this is one of few projects that seem ready to go so I need to learn quickly before the cold comes.

Mark Eatherton

Could be either or...

Open loop direct connected to the tower, or closed loop indirectly to the tower. You need to do some home work. That height calls for a fill pressure of around 28 pounds, and when you add the usual 5 PSI to the mix, it puts your bottom pressure over the holdback capacity of a 30 PSI relief valve :-)



If all tubing in the systems is plastic, it cold be an open loop. If the mains are steel, probably (hopefully) closed loop.



You need to do some more homework. I've also seen these systems serving as fire protection systems, so be careful about emptying the system out until you know for sure. If you trip the flow switch, you get to meet the Fire Marshall. Been there, done that, have receipts to prove it :-)



ME

Jason Quinn

Closed Loop

I spoke with a maintenance guy at the project and he says that on October 15th they close the valves to the chiller tower riser and open up the valves from the boilers, the "inside loop" as he referred to them. The piping in the boiler room is labeled, "Tower Loop" and "Inside Loop". From what I am gathering, the chiller and boiler "riser" piping is separated by valves, but they share the water distribution loop? The mains are steel.



Correct me if I am wrong, but if the highest heat pump is 40 feet up, isn't that a static fill pressure of 17 psi + 5 psi= 22 lbs? Thanks again.

Mark Eatherton

Only if....

If there is a heat exchanger between the inside loop and the cooling tower, then yes you are correct. But if it isn't isolated, and requires system water pressure to get the water up to it, then you have to use the highest SYSTEM elevation for your fill pressure.



ME

Jason Quinn

Heat Exchanger.....

I actually found a heat exchanger "scrapped" in the corner of the boiler room today. It looked in reasonably good condition and fairly new. Could someone have removed this from the system where it used to isolate the tower from the inside loop?

Mark Eatherton

Could be...

Cooling tower may have its own internal heat exchanger circuit that is tied to the closed loop portion of the system. It would also have a separate tower loop/sump to enhance heat rejection.



Maybe the tower has been updated ???



You said "I spoke with a maintenance guy at the project and he says that on October 15th they close the valves to the chiller tower riser and open up the valves from the boilers, the "inside loop" as he referred to them. The piping in the boiler room is labeled, "Tower Loop" and "Inside Loop". From what I am gathering, the chiller and boiler "riser" piping is separated by valves, but they share the water distribution loop? The mains are steel." This would indicate to me that the tower loop is directly connected, and if this is the highest component, then it would dictate fill pressure requirements.



How do they keep the tower from freezing in the winter?



ME

Jason Quinn

Time is moving on....

Time is moving on and the contractor is pressuring me for a price as the cold weather is near. That being said, I want to make the right decisions here and do the right job.



Is a safe approach for me to figure the project with a heat exchanger isolating the boiler and the water loop? This should also allow me to figure conventional cast iron boilers and monitor return temps so that I can utilize the existing chimney, correct? As previously mentioned, venting a mod-con is nearly impossible in this building.

Mark Eatherton

Yeah but....

Why put in a heat exchanger if it is not necessary? The heat exchanger that was between the steam boiler and the system is not going to be big enough, unless you replace the steam boiler again, and that probably won't show much energy savings...



Good things take time to think them out and do proper research. Mod cons are available in sizes up to 1.5 mil these days, and more if you don't mind aluminum heat exchangers.



If ownership REALLY wants to save a butt load of money, they will allow you the time to research this job and do it right. Otherwise, why not just throw in another steam boiler.



Savings of 30 to 50% are a real possibility on a job of this nature.



ME

Jason Quinn

You're right.....

I guess I am getting frustrated because I am having difficulty wrapping my mind around this project and the relationship between the cooling tower, the boiler, the piping etc.



I am going to set up a site visit with a manufacturers rep to try and gain insight also. In addition, I will continue to research and read to educate myself so I will know better what I am looking at. All of the insulated piping in the boiler room is hard to decipher. Thanks for the "reality check"

icesailor

Boiler renovation:

This is strickly MY opinion and probably not worth much.

This sounds like a very complicated job and was origonally designed my a ME/PE (Mechanical Engineer) and needs to be all ASME approved. It seems to me to be in the realm of specialty contracting. I am in no way suggesting that anyone here is not capable or qualified to do this job but it sounds to me like it is very complex in its design and operation. It also sounds like a contractor has promised something that may not be possible or practical. And wants someone to make his promises come true.

If this job is in Massachusetts, and it is a public building, the plans may need to be approved by the Dept. of Public Safety and it will surely need to be inspected annually for conformity. It sounds to me like the makin's of a first class genuine fluster kluck. If it doesn't work, you will own it. If they want to spend buckets of cash on this project, they shouldn't be so cheap as to not have a Professional Engineer design and spec this project.

If you did this work exclusively, you wouldn't be asking these questions. You would also be working off designed plans from  PE. This should have been in the works last Spring, not the middle of September.

You could really be hurt in this job. Someone else should take the responsibility for this design and specification, not you. You get a lot of really good advice here. But no one here has actually cast their evil eyes upon this work of wonder.

JMHO,

Jason Quinn

I appreciate your input Icesailor

Yes, as I mentioned at the beginning of this thread, I am unfamiliar with water source heat pump systems. At this stage of the project there isn't an MEP's design. Right now, they are asking for my input and to price the boiler room equipment installation. They will need an engineer to draw plans to file for the permit. I don't know why they did not start this process in the spring, although I too have asked this question.



Would other pro's require MEP plans upfront before engaging a project like this?

icesailor

Water Source:

I am quite familiar with a renovation that eliminated a large fossil fueled heating boiler for a state of the art "green" system for the renovation and addition. There are areas of the new structure that will not heat or AC because of HUGE, obvious infiltration factors. Most folks are dressed for the season in the building. Four ground water wells were drilled to give 160 GPM of well water. The system is really electrically driven. Electrical back up. There are complaints from the ownership which I am not in on. But the electrical bills for operation average $30,000 per month and the building has won some "green" awards and design awards. The owners haven't commented publicly.

The "Pro's" are all to quick to take credit for a great job and give no credit to where it is due. To "We" who turn these plans into reality. But these same "Pro's" are nowhere to be found when it doesn't work and quick to pass the blame on to the installer for "Air Excuses". Reasons that defy the laws of reason and physics.

JMO.

CMO

Jason Quinn

I understand

just to clarify, by pro's in my post, I was referring to professional installers; namely those that interact on this forum.



I was posing a question to others to get their feedback.

Mark Eatherton

I don't generally depend on engineers...

It is my job to have a full and complete understanding of what I am dealing with. If in doubt, I will study until I am satisfied I know what I am dealing with.



In certain cases, the use of an engineers stamp is required, and when required, I have numerous engineers who will review and stamp my designs.



So, as with any hydronic heating question, the only correct answer is, "It Depends" , but you already knew that :-)



ME