The case of the tardy two pipe system

RayWohlfarth

The school needed to replace the hydronic boilers on the two pipe system. The two pipe system uses heated water in the winter and chilled water in the summer. As you know, the time it takes to changeover from heating to cooling. It could take several hours or even a day. This type of system of system gets lots of comfort complaints in the shoulder times of the year when the building needs heat in the morning and cooling in the afternoon. Normally, I would recommend a condensing boiler for those shoulder days but we could not on this project. The owner stipulated a heating system which could change from heating to cooling more quickly. What would you do? You’ll find my solution on Friday at 6am est.

EBEBRATT-Ed

Switching quickly is a problem you have to get rid of the heat in the water. Starting the chiller with warm water will overload it and it will trip out.

I would pipe a "dry cooler " into the system and let the outside air cool the water down enough to get the chiller on line. Have to have the controls to accomplish this as well.

Daveinscranton

Could this be a place for evaporative cooling of the roof?  Essentially a sprinkler on the roof.  Cheap.  Drain the piping in cold weather easily if the piping is pitched correctly.

clammy

I don’t dabble much these days in larger system as such but from my point a two pipe combo system as you describe will always suffer on the swing season being can’t make everyone happy .When asked I always say for real comfort and control you need a 4 pipe system w 3 way valves and sa sensors to make it all happen . But these days in a cost saving effort everybody just does a two pipe w zone valves no 3 way no nothing usually just in and outjust like a a terrible burger joint ,and hear the complaints on the shoulder month before a shut down cross over but they saved a ton load of money on the original install and suffer forever on shoulder crossover season . I ve witnessed some load match systems using a single two pipe system and when the complaints can in we just past it right back to the original installer and never worked on the chiller or hot water system . Basically there was not much you were gonna do without a ton load of money . I would guess using some outside air and a decent ecomizer enthlaphy controller one could get some free cooling from outside air and re temper to desired indoor air temp but this again would not be cheap nor depending upon the design possibly impossible depend upon access to outside air . Unfortunately so much is price driven as for the original install the cost of a 4 pipe system would have been over the top . Look forward to your fix .
Peace and good luck clammy

ratio

Oh, oh! A (or several) heat recovery VRF system(s)! Been doing these lately. Very neat, the Trane/Mitsubishi system will heat and cool, at the same time, with only two pipes to the branch box. I think it's magic.

RayWohlfarth

Lots of great ideas. What I did was to furnish three boilers, two of which were combination boilers. The boilers have an internal coil typical used to heat domestic hot water. The coil side of the boilers were the lead when the loop temperature dropped below 140 degrees. Above that, the flow went into the space heating side of the boiler. It worked well for the customer. Here is the link for video. https://youtube.com/watch?v=rbDkIIBhOJE