When Water-To-Water Heat Pumps Don’t Work Well

August 23, 2002
/ Print / Reprints /
ShareMore
/ Text Size+
“Dear ASHRAE:
“A building I am working on has an existing chiller-boiler arrangement. The owner wants to install a water-to-water geothermal system, but wants to use as much of the existing system as possible (ventilators and fancoils). Is this possible? Will the geothermal system work as intended?
— Signed, Nervous Engineer”

This isn’t a letter from a syndicated advice column. It’s from a forum on “Water-to-Water Heat Pump Operating Problems,” held at the 2002 Annual Meeting of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) in Honolulu, HI.

One of the problems with water-to-water heat pumps, it was acknowledged, is that they need a volume of water flowing at all times. Their biggest advantage is that the heat pump never “sees” the building’s load; it sees the water loop. The water loop is what sees the building. Therefore, water-to-water heat pumps “can work on a retrofit and you don’t care how people use the building,” commented an engineer.

However, “We’re always running into water-flow problems,” stated another mechanical engineer. The system “has to have adequate evaporator and condenser flow; otherwise, units lock out on high head pressure.”

When adding a water-water heat pump system to an existing building and replacing its HVAC system, the problems that arise can be attributed to “the whole issue of commissioning,” an engineer stated. “It’s the lack of understanding by people who have always dealt with a boiler and a chiller.”

CONSIDERATIONS

“One job I was on had seven ‘cooks,’ and it looked like we wouldn’t get any broth,” recalled a forum participant. “One ‘cook’ demanded an economizer cycle. That was OK, and the controls guys designed it that way, but at that time, no water was circulated [and] no water was available for the zones that needed it.”

System integration and zoning are possible, but system limitations need to be spelled out clearly to decision makers. For example, it may be possible to design for a north zone and a south zone, but not in adjacent rooms. And “Nothing says we can’t mix and match water-to-water and water-to-air systems,” said an engineer.

However, “We have uncovered design flaws from trying to reutilize the existing system,” specifically the low-side pumps, stated an engineer. “We didn’t take into consideration the pressure change.”

In another case, a 40- to 50-year-old system wasn’t flushed out properly before the combined system was started up. New components were damaged downstream.

Finally, problems can result if the existing system itself was oversized — not an uncommon occurrence. “We have yet to find an old radiant system that didn’t have the terminals matched to the boilers, and the boilers were oversized,” stated an engineer.

Most importantly, though, “In water-to-water systems, water flow is a key issue. We’re seeing things with three-way valves involved, or trying to design geothermal when they don’t use antifreeze; then we see cracked heat exchangers from the freeze-up.

“A lot of things can be resolved if you really look at your application.”

SUMING IT UP

“Dear Nervous Engineer:
“Geothermal is wonderful, but if the owners want to keep the old boiler in there, maybe it’s best to just say no.”

Publication date: 08/26/2002

Did you enjoy this article? Click here to subscribe to The NEWS Magazine

Recent Articles by Barbara Checket-Hanks

You must login or register in order to post a comment.

Multimedia

Videos

Image Galleries

2014 Energy Efficiency Forum

Highlights from the 25th annual Energy Efficiency Forum in Washington, D.C.

Podcasts

NEWSMakers: Jeremy Begley

Jeremy Begley, home-performance specialist and Web and social media manager with National Heating and Air Conditioning Co. in Cincinnati discusses how and why you should add home-performance philosophies to your contracting repertoire. Posted on Sept. 12.

More Podcasts

ACHRNEWS

NEWS 09-15-14 cover

2014 September 15

Check out the weekly edition of The NEWS today!

Table Of Contents Subscribe

Venting R-22

The NEWS reported that a man received prison time for venting R-22. Should EPA step up enforcement?
View Results Poll Archive

HVACR INDUSTRY STORE

plumbing-hvac.gif
2014 National Plumbing & HVAC Estimator

Every plumbing and HVAC estimator can use the cost estimates in this practical manual!

More Products

Clear Seas Research

 

Clear Seas ResearchWith access to over one million professionals and more than 60 industry-specific publications, Clear Seas Research offers relevant insights from those who know your industry best. Let us customize a market research solution that exceeds your marketing goals.

DON'T MISS A THING

Magazine image
 
Register today for complete access to ACHRNews.com. Get full access to the latest features, Extra Edition, and more.

STAY CONNECTED

facebook icontwitter iconyoutube iconLinkedIn i con