heat pump for space heating 2

[oooaaa]

in a 6 story office building project, people sugest we could put a water to water heat pump on the interior zone system, therefor trnasfer the waster heat to the air handling units serving the exterior zones in winter and off season. Is the hot water generate by the heat pump at 105 to 110 deg F high enough for air handler or fan coil units to heat the space?

 

[MintJulep]

This type of system is used, but in my experience is not very common.

To be successful, the configuration of the building really has to have the right ratio of interior to exterior space. The concept is that interior spaces tend to need cooling year-round due to internal loads and lack of envelope losses, while the spaces that have exterior envelope contact need heat.

I have seen such systems mis-applied in long narrow buildings with essentially no interior space - total disaster.

Utility rate structure must also be looked at closely.

 

[ChrisConley]

The water is hot enough for the application, but you'll need a lot of coil.

Like MintJulep mentioned the balance between interior heat generation and perimter heat loss is tough to get.

More common is when heat pumps serve the interior and exterior zones. A neutral temperature loop circulates with a boiler to increase temp and a cooling tower to reject excess heat as required.

In that setup interior heat pumps reject heat to the loop, which can then be used by exterior heat pumps.

 

[MintJulep]

The disaster system I mentioned earlier actually had the neutral temperature loop that Chris mentions.

Unfortunately for that system, the building was all exterior, so all of the heat input to the loop was from a massive central hot water generator, running at ridiculously low temperatures, and short cyling. The low temps caused condensation of the flue gas, and as the equipment was not designed as condensing equipment - well it aged prematurely.

I recommended converting all of the heat pumps to DX cooling only, adding hot water coils for heating, and upsizing the fans accordingly. Even with the necessary replacement of the boiler, payback was under 10 years.

The other problem with this type of system in general is that the "neutral" temperature is off of the best efficiency point for both the condenser and evaporator side of the heat pumps.

The whole thing is thing is just terribly inefficient, and uneconomical unless the utility rate structure is unusual.

Might work if you had a local co-gen plant, feeding the waste heat into the neutral loop to supplement the heat from the interior spaces. Probably even harder to obtain the right building layout balance though.