I'm building a house in Argentina where the traditional way of cooling is with split ACs and where underfloor hydronic heating is very common.  The house will have a flat roof with lots of space to hide external units.  So there is no issue of aesthetics for either the interior or exterior units of the mini split ACs.

I'm trying to build a *very* efficient house, and I'm trying to figure out what is the most efficient way of heating and cooling between two options:

a) Air to water heat pump with the hot water going to underfloor hydronic heating, plus cooling with fan coils connected to the same system.  The underfloor heating would be in 5 zones.  Systems available here are the LG Therma Water V and Daikin Altherma (both air to water heat pumps).  Because of the humidity in Buenos Aires, underfloor cooling is not possible, so fan coil units (7 probably) would be installed for cooling;

b) Split heating/cooling units for each bedroom, the living room and kitchen in the house - 7 split units.  The idea would be to install intelligent minisplits like Daikin has with wifi capability and motion detection to program different levels of heating and cooling depending on time of day and whether a person is in the room or not.

I am being told that option (a) is more efficient because the temperature of the water that passes through the floors is lower and so with a lower difference between water temperature and outside air, the efficiency of heating is better with underfloor heating.  That might be true, but it seems like it doesnt address the cooling part of the equation.

When I look at the specs of the LG Therma V or Daikin Altherma systems, for cooling the EER is really low - like around 4, which would mean an SEER similarly very low.  Whereas if I look at say the mini splits of Daikin, they have ones with SEER of up to 24.5 and lower priced one with an SEER of around 18.  So for cooling, the air to water heat pump systems have an SEER of less than 4, but the individual splits have SEERs of 24.5.  That seems to be an enormous difference.  Wouldn't that mean the cost of cooling would be many many times more with the air to water heat pumps than with the individual splits?  What am I missing?  For heating, the COP numbers seem to be similar for the two different systems.

Besides the higher cost of installing zoned underfloor water pipes throughout the house, I can't understand how people are telling me that it will be much more efficient in the long run to go with the air to water heat pump with underfloor hydronic heating and fan coils for cooling.  I must be missing something.  Help!

I have just started learning about hydronic systems and am planning on doing an air to water heat pump with ductless air handlers in each room.

I think a lot of the efficiency of the newer systems comes from part load conditions where it is cooling/heating a smaller delta T vs 100%. Because of this the COP has a very large range depending on the operating conditions.

From what I can tell SEER does not give the best picture for comparing a regular mini split to an air to water heat pump. You might try looking at COP values of different systems at the exact same conditions (might be hard to find the data for comparison).

You might find this helpfull http://www.chiltrix.com/documents/IPLV-NPLV-Explained-Comparison.pdf

Hopefully someone else can chime in to better answer your question.

I don't know what's up with the oddly low EER values, but they shouldn't be compared to the other values.

I expect that hydronic cooling with fan coils should be around the same efficiency as an air-air system. Heating with a very large heat exchanger (like a floor) will provide some efficiency improvement. But probably not enough to pay for the initial cost difference. On the other hand, hydronic is easily zoned and fairly easily time shifted (if you have time of use electricity pricing).

Yes, before you can compare economics and performance of cooling and heating appliances, you first have to convert Average Fuel Utilization Efficiency (AFUE), Energy Efficiency Ratio (EER) and Seasonal Energy Efficiency Ratio (SEER) to Coefficient of Performance (COP). To convert AFUE to COP, divide the AFUE in percent by 100 to obtain the COP. For example, an AFUE of 96% equals 0.96 COP. EER is typically calculated as 1.12 times the SEER minus 0.02 times the SEER squared. For example, 13.0 SEER equals 11.2 EER. COP is calculated by dividing the EER by 3.412. For example, 11.2 EER equals 3.3 COP.

In addition to cooling and heating appliance performance, fuel cost should also be considered to ascertain operational cost. With both cooling and heating appliance acquisition and operational costs determined, one can perform a Return on Investment (ROI) analysis that also considers the expected appliance maintenance cost and expected appliance lifetime to select the most economical cooling and heating appliance for a given locale. We have some calculators on our website that can assist one accomplish this:

Borst Integrated Cooling System Performance Calculator

Borst Integrated Heating System Performance Calculator

SEER: Sales Executive Efficiency Ratio

EER: Engineer's Efficiency Ratio

COP: Complete Others' Performance ratings around the globe to 100% electricity = COP of 1.0 (now x 'on the dollar' per hour)

If not yet read: Please see ASHRAE 2002 Journal LIMITATIONS OF SEER..." review of " 18 SEER to a 10 SEER" in various conditions by "Dr Steve Kavanaugh's SEER ratings" reports, or maybe some others covering "high SEER's" and ACCA questioning 'swampy southern homes' having blowers on just too high of an air speed, just not dehumidifying, as many have seen