Heat pumps: Minimal return water temperature while heating

[IcerCRO]

This is not meant as a question that actually requires a straight up answer in degrees, but more as a conversation topic.

Let's say the heat pump in question is air source for the sake of conversation, but it's not relevant. The system however is hydronic, with floor heating (and fan-coils etc.). It is used in heating.

I'm wondering what the lowest return water temperature to the heat pump is (the condenser). What are the guidelines I have to follow to understand the logic behind the system?

I thought the lower the RWT the better, compressor just goes to higher RPM, and if the LWT is not reaching set point after RMP max is reached the electric heaters kick in.

I'm asking this question because a Daikin technical representative told me that their Altherma units don't spin up the compressor only until after 20-30 degrees of return temperature is reached. Until then, only electric heaters are used.

This is both worrisome and illogical to me, so I'm wondering if this is a rule or an exception.
I have to create systems which will most likely have floor heating cold-starts a few times per winter, so this becomes an issue.

Can anyone shed any light on this subject?

Cheers

 

[EnergyProfessional]

condensers/evaporators require minimum/maximum temps to provide minimum lift. your manufacturer can tell you that. Go to a different manufacturer if you think Daikin is not cutting it. Some units have internal control valves (reducing flow) to maintain certain temps, other may use other strategies incl. shutting off like Daikin seems to do. Try Mitsubishi if they have a solution. Obviously if the manufacturer says so, you should obey. they should know their equipment better than we do.

 

[NoHtPp]

Hi Herr: I have also greatly enjoyed your posts!

As a GTHP nut, though, if not for sake of "air source" simple dual compressor technology pioneered by HYDRO-TEMP.com of AR and primary looping back , to the HP, helps a lot. [not o confuse with hydro-delta, -hydro-heat, as some will do ]

Smaller reservoirs are required with VFD Iq Variable compressor drives and dual unit or dual compressor systems that get to the specifics "QUICKER" or hold them at temps for ANY inducements that do not push all the loads beyond manufacturer specs.

Just for an application of slab basement and floor radiant, AND radiators (existing) there is NO RESERVOIR on VFD 5ton (actual 61k output compressor label) called a "size 6" in salesy terms, which allows for a first "on" load always over 65% of the soft starting "spin-up" of the FD such that say, it always runs in start ups over 8 minutes and usually over 12 minutes. -- a decent minimal cyclic use... is 12-14 minutes, just to get some great HP efficiency.

What are you doing with what the KY Schools in zone 4 found in near 0 weather , testing Daikens and not going there? The VFD Water Furnace, ClimateMaster, Trane, and Hydro-Temp (AR) are all likely to continue to out perform AHP on - North...

http://www.energystar.gov/index.cfm?c=most_efficient.me_geothermal_heat_pumps

NOTE: Closed LOOP highest efficiency's are all some OEM's care to list therewith already being the most efficient rated, and
that does not include 100% Heat Recovery to Hot Water from a FORCED AIR HVAC-On-Demadn-HW-Priority that works in Cooling and ON Demand as an instant HW heater, shooting COP's in to high 6's and SEER's above 50's and EER's into the 50's , on rated EER's units of 40+ 's you can read about.

 

[NoHtPp]

NOTE: Those high EER's above Energy Star Closed Loop ratings are AHRI raw data. EER's 40+ are about of the low staging and middle stages in the then "double-sized" heat-exchanging surface areas of water coils and air coils. MO' Metal to compressor is about : compared to a small (of duals, doing 3 staging) compressor function or low speed -mid VFD operation that occurs 65%-75% of the total running hours. Such EER's are common in loading then of - units sized to and a little closer to peak requirements of some condition.

Heating a swimming pool ? --- that heat from air conditioning-cooling is doing what all summer?