WSHP vs. Boiler/Chiller AHU 4

[Ziggypump]

I'm looking for some help, direction, or knowledge on life cycle cost analysis. Comparing a water source heat pump system to a boiler/chiller air handler with a cooling tower. The client is looking for some information, and someone is in their ear saying that the heat pumps will need to be replaced in 10 years. This seems outrageous, but with this being a 40k sq. ft. single story building, the air handler system is out of place.

If any one can help, I would appreciate it.

 

[Drazen]

it would be easiest for you to show your client capacity range of the mentioned heat pumps so he/she will hopefully understand that it is not expected to be applicable for such larger projects.

such ideas often comes from media torture how heat pumps and renewable energy solves ALL problems, and whoever is not totally committed to that is declared as decadent.

 

[317069]

Heat pump is a good idea, but in your case, 40000 sq.ft single story building, why don't think of rooftop units and get rid of water pipes problems.

 

[Ziggypump]

They want LEED Silver, so packaged dx rooftop units are out, and there's some anti-anything on the roof that we can't get past.

 

[EnergyProfessional]

do you mean geothermal heatpumps? If you mean just a water source heatpump where a boiler inject heat, those are quite expensive in heating. they mostly are used in commercial space to submeter. If it is all the same owner, a larger plant is better.

I think you need to explain more what it is you have to do. climate, heat rejection etc.

To know what is the better option to operate you need to run an energy simulation with Trane Trace or some other professional tool. there sin't a rule of thumb, it depends on if you have simultaneous heating and cooling and for how long etc.

 

[MTES93]

Herr, hit it w/ the simultaneous heating and cooling. That is where heat pumps really are beneficial. On a typical tower-boiler system, you really need to look at your heating fuel costs and see if you will save as much as you think. A water source (pump and dump) or ground source (bore field) you do get much better heating and cooling fuel savings but the costs can get expensive for the well(s)/bores. W/ the latter you need a pretty good sized field. With the former you sort of take your chances hitting a water source and more importantly get the dang water BACK in the ground. We did the open system at our office and while the energy savings are huge (we cool directly w/ the water via radiant and don't run compressors), we did have a heck of time getting the water back into the ground.

As far as heat pump lives, I think 10 years is pretty short w/ today's quality heat pumps. I would estimate 15 years is a good guess and ASHRAE has commercial water to air heat pumps anticipated service life at 19 years. Contact a few mfgrs.

At the risk of opening a can of worms, you could look at VRV systems for this size of building. Depending on your climate you may need auxiliary heating if you use an air source system.

As mentioned, evaluate using energy simulation, gather costs and provide a quick life cycle cost of a few options.

And I agree w/ Drazen, sometimes the best solution is the tried and true and the 'pushing' of green design is getting a bit out of hand.

My two cents.

 

[Ziggypump]

Water source heat pump (boiler/cooling tower) are the preferred method right now. I know 10 years is way short with what can be expected. An ASHRAE document showing life span of equipment (2011), lists commercial heat pumps with 24+ years. We are looking for maintenance type numbers, or if someone has done a comparable life cycle cost analysis for comparison.

Due to the LEED request, we don't see how the owner requested air handler system described in the beginning would even get to a LEED prerequisite, thus nullifying any LEED points gained (10% over baseline for new buildings). Thought about VRF, but was vetoed; the idea of rooftop units is looked down on, but an ERV on the roof is a acceptable; geothermal would be nice, but upfront cost excludes this option.

I know that a boiler will run up cost for this type of system, but the heating loop doesn't need to be anywhere near 100 degrees F let alone 140. We are looking at maintaining 60 degrees in the winter and around 80-90 in the summer. Both boilers and cooling tower will inject water into the heat pump loop, leaving the possibility of some free heating or cooling within the building.

Not too sound harsh here, but with the given constraints, we believe this is the best system for the requirements. Now we just have to sell it the head honcho for final approval (why it has to happen now is still unknown, would have thought this should have been taken care of long ago) and they have a lot of misinformation that we need to correct.

 

[cry22]

Ziggy
You did not answer basic questions by Herr
Climate location
Building use - office? warehouse?

Since your temperatures are outside the normal range (60 winter and 80-90 in summer) one would think that this is a warehouse, not an office space.

With such data, you should start thinking outside the box. The heat pump/Boiler business should not be cast in stone.

Regardless, I would look into some other alternates:

1. Evaporative cooling - preferably Indirect/direct - you will supply air at WB temperature and will do you just fine for the 80-90 indoor temperature. simple, cheap and efficient.
2. Radiant heat - gas-fired is really cheap and effective (50% savings over conventional heat-it really works great) - Or,
3. Condensing boiler with in-floor HW radiant heat for new construction.
4. For LEED, you should consider Solar thermnal for the in-floor radiant heat (you have 40,000 SF of roof and all you need is low-grade heat for in-floor radiant heat) - not so expensive and will get you some serious LEED points (probably cheaper than the boiler business).
5. Talk to your architect, Cool roofs are getting really good results, again 40,000 SF of roof - OR,
7. Consider green roofs (Your roof load is substantial) more LEED points for storm water, less cooling load.

In summary I'd consider

Green (or cool) roofs/Evaporative Cooling/Solar thermal for HW in-floor radiant heat (push come to shove, use gas-fired radiant heat). If you go cool roofs instead of green roof, consider collecting rain water for use as make-up for evaporative cooling.

NOW, That's sustainable, you should be good for LEED Gold.

 

[EnergyProfessional]

heating via boiler-injected heat will be less efficient than using a boiler only unless you have a lot of cooling in heating season.
think about it, you burn natural gas to heat water, and then you add electricity (heatpump) to get that heat into the sapce from the water. If you just have aa boiler (and radiators let's say), all you need is natural gas. with the heat pump your natural gas consumption is a bit lower, but the electricity you need to add heat is more costly.

In addition all these little heatpumps sure are less efficient than one large heatpump, like a chiller. so your cooling cost will be higher. Again, if you have simultaneous heating/cooling this equation is different.

you really need to do an energy simulation with Trane Trace or some other professional software. We can't really decide that, especially without knowing more about the application.

I also imagine maintenance on multiple small heatpumps must be more costly than a few central devices.

You also could do a 4-pipe heating/cooling system with in-space fan units and a central chiller/boiler plant. the chiller could do heat-recovery if this is useful or can work as a central heatpump, keeping all your maintenance in one location. (of course, any in-space cooling will require condensate piping, filters etc.)

If you care about your client, forget about LEED. Those credits are skewed. If you use a gas-boiler, the base case is a gas fired system. If you use heatpumps, the base case is electric heat. so you magically always will get many more points when using heatpumps just because then you can use a much less efficient base case. LEED was developed by landscape architects and interior designers, not by people who actually know anything about buildings. It is a green building Mafia scheme, it is just about USGBC and all the consultants getting money for paperwork. there is no verification, you can submit anything you want. you can even a building certified that doesn't even exist (as long as the money you feed them exists). when we work on buildings over $100K goes to LEED fees (USGBC, consultants) and guess where that money comes from ? Exactly, from measures that would save energy. So in order to get LEED certified we have to spend less money on proper HVAC equipment.

 

[Ziggypump]

What does the location really matter?

I'm not answering the questions? You're not even helping. I was looking for cost analysis that someone might have done somewhere regarding maintenance and possibly install cost. I know the utilities cost and requirements, that can be estimated out. The time for needing help is passed. This is why I got on to ask. There wasn't enough time to do a thorough, proper job. The owner was just looking for some numbers to compare. This is one of those instances where exact detail isn't needed.

The type of system being installed IS NOT up for debate. I know this heat pump system I highlighted isn't the most efficient system, but it is the most efficient system that we can get away with and match the owners requirements. If I learned this incorrectly, then by all means, please speak up, but to design a system takes more than simple knowledge. You need to incorporate the owners requests and budget. MONEY TALKS!

As far as larger heat pumps being more efficient go, that's total bull. Smaller heat pumps have greater efficiency. Look it up, 5 tons and smaller all have about the same efficiency, 6 tons slightly less, and it's all downhill from there.

Who cares about water temperature for a building when you have heat pumps? yes the lower heating temp will not get as much heating capacity from a heat pump, but look at the manufacturers information. The difference between 70 degree water and 60 degree water is that the 60 degree water will supply 3 MBH less than the 70 degree water? Unless you are sizing really tightly to the you load calculations, this will have little or no bearing on the system.

Radiant heating is going to be a factor, but final design is still up in the air. If no one can help with some cost numbers, please don't waste my time with this mindless blather.

 

[EnergyProfessional]

I'm sorry we wasted your time with our free advice.

I'm curious to know how you are able to "estimate" the energy cost without knowing the climate, load profiles and without energy simulation.

and who cares about fluid temperature for heatpumps, since COP always is constant regardless of load and temperature....

 

[Drazen]

"who-cares" lowering supply temperature from 70 degree to 60 degree presents 25% less capacity, which comes close to heat pump capacity loss at all but mildest days of cooling season at the same regime change.

if such a figures you deem negligible, i do not understand what kind of figures are you looking for. your talk resembles talk of "hasty" client who wants to spend 5 million euros on making decision, but do not want to allow engineer's five days for analysis.

such kind of client ends with major decision being made by fitter's advice. they never have time for engineer, neither engineer can hope to have successful business with such guys. i

i could count at least dozen guys with such approach, seeing them going into bankruptcy few years later.

 

[Ziggypump]

I like how you're "Free advice" wasn't requested. Is that even advice then? Energy costs are my issue, and there's a lot more to determining a life cycle cost analysis, but I guess HERR and Drazen don't understand what is all involved. I know energy analysis. I've done them. I don't need advice on how the COP and efficiency are impacted by these temperatures. Have any of you done a geothermal system? I have, and the winter temperatures can get way below 60 degree F for the water. Lower temperatures do impact the heating capacity, but it's not an insurmountable issue.

Drazen, look up the specs for a heat pump. A 5 ton unit between at 60 degree water is 3.3% less capacity. Where is your 25% less capacity coming in? Are you even looking at heat pumps? Or are you looking at a regular water coil? A water coil and heat pump are 2 totally different systems.

Look at the first post. I needed help with some cost estimates relating to LIFE CYCLE. I don't need an efficiency lecture on how terrible the system will be.

Drazen I will agree with you on the terrible situation of not being allowed to do a full study. But this is the clients show, and fast numbers are all that are needed. Also, this is the clients request, not our stance on the project.

I have noticed a trend on this forum where people give their "ADVICE" by tearing down the system that is only partially described. Advice wasn't asked for. It isn't needed at this moment of the design for the building. I needed some INFORMATION that someone might have. If you don't have any INFORMATION, then I don't need to know that the described system will SUCK, and that I'm putting the client in a terrible position.

Bonus points to anyone that can help me close this thread. It's gotten totally off course, and I'm sick of being put down by specialists and their "ADVICE".

 

[EnergyProfessional]

We are not putting you down, we just ask more questions to better understand and advise.

After all you came to a forum on the internet and asked for advice and we felt with the information given we couldn't give good advice. And apparently our advice wasn't good enough.

If our free advice isn't good enough, why don't you hire a mechanical engineer to advise you and your client?

 

[317069]

Ask an engineer in your company to help you for this, it looke like this task or homework is over you ability.
people here trying to help each other, Cry gave you very important advise.
I wounder how a company like your company had been hired to do this job and they are not able to do cost esimation or other design tasks, this forum is to exchange knowldges not to provide free online design, so if you are not able work with it, so easy, do not ask. you can read ASHRAE or other referances about life cycle, contact manufucturer discuss with them and kiss your client hand if you want, but when you come here you have to be polite and respect any member tried to help, by the way you could use RTU with energy exchanger to save energy and get LEED or FEED or REED or what ever you want to do.

 

[dbill74]

Ziggy, trying to get back to your OP about life cylce or as I read your question, life expectancy is what you are looking for. There are a number of factor's that go into equipment life expectancy as I'm sure you are aware, not least of which is location; not just project location, but equipment location. Since you already ruled out geothermal, that means you will of some equipment outside.

Unless the building is a barn, hanger or warehouse where the doors will be open for extended periods of time, I don't think it unreasonable that well maintained indoor equipment (AHU's, boiler, chillers, etc) can last 40+ years. However, it is the outdoor equipment that is going to really take a beating. If you are near the coast, salt air can really shorten equipment life expectancy. If you are looking at an outdoor condensing unit/heat pump that is near the coast without a protective coating on the coils to protect from salt air and is not cleaned regularly, then I would agree that 10 years is a reasonable life expectancy. However, that same equipment with a protective coating and is cleaned a couple times a year should last 20-30 years.

Hope this helps.

 

[Waramanga]

There is plenty of lifecycle stuff out there, no need to invent anything. Find the closest bit of kit in the lifecycle table from your prefered scource and use that. Lifecycle has so many variables. small dx stuff has a short life, its cheap so make sure its easy to replace.

 

[urgross]

Attached site may be useful in support of expected equipment life and anticipated O&M costs. I find it useful (along with 2011 ASHRAE HVAC Applications) for LCCA.

http://xp20.ashrae.org/publicdatabase/

I deal a lot with the RTU issue, but for new construction have occassionally been able to allay fears by including a Structural PE stamp. Sometimes that doesn't work, seems to go randomly by day of week.

 

[willard3]

My advice to you is to light a bonfire for heat and get a block of ice and a fan for cooling.......nothing with lower life-cycle cost.