R290 vs R32: high-temperature heat production, DHW and the role of PCM thermal storage

The R290 vs R32 comparison has become central in the debate on next-generation heat pumps. Designers, energy managers and industry professionals are asking which refrigerant is best suited for high-temperature heat production, for low-temperature heat production and, above all, for domestic hot water (DHW) production.

The discussion often focuses on the individual unit — R290 heat pump or R32 heat pump — overlooking a fundamental aspect: real-world performance depends on the system as a whole, not just the refrigerant. In particular, managing DHW temperature and DHW demand peaks is the real design challenge.

In this article, we technically analyze the R290 vs R32 gas comparison, explaining why, in many cases, it's not necessary to push the heat pump to 60°C if the system is properly designed and integrated with a PCM thermal storage.

R290 vs R32 gas: basic differences

In the R290 vs R32 gas comparison, the two refrigerants have very different characteristics:

• R32
  • HFC refrigerant
  • GWP (Global Warming Potential) ≈ 675
  • Widely used in air-to-water heat pumps
  • Good efficiency in low-temperature heat production
• R290 (propane)
  • Natural refrigerant
  • GWP ≈ 3
  • Excellent thermodynamic performance
  • Ability to operate at higher supply temperatures

These differences explain why R290 heat pumps are often associated with high-temperature heat production, while R32 heat pumps are considered more suitable for standard low-temperature systems.

High and low-temperature heat production: what does it really mean?

When talking about high-temperature heat production, this generally refers to supply ≥ 60–65°C, typically required in:

• systems with traditional radiators;
• retrofits without emission upgrades;
• DHW systems with high storage temperatures.

Low-temperature heat production, on the other hand, refers to supply between 35 and 50°C, ideal for:

• radiant panels;
• fan coil units;
• modern high-efficiency systems.

The key point is that domestic hot water production does not necessarily require the heat pump to constantly operate at 60°C. This is where a common design mistake often arises.

DHW and heat pumps: the real issue is not temperature, but peak demand

The DHW-producing heat pump is not an instantaneous system. Even when talking about hot water with a heat pump, the limitation is not so much the maximum reachable temperature, but rather:

• the power available in the short term;
• the ability to handle concentrated demand (simultaneous showers, turnover, morning peaks).

For this reason, many systems try to compensate for the issue by increasing the supply temperature (e.g., 60-degree heat pump), with direct consequences:

• reduced COP;
• greater compressor stress;
• increased electricity consumption;
• need for larger and more expensive units (high-temperature air-to-water heat pump prices).

Operational limits of heat pumps without storage

Without an adequate storage system, the heat pump is forced to:

1. follow the instantaneous load;
2. frequently operate under non-optimal conditions;
3. undergo continuous on/off cycles.

This applies to both R290 heat pumps and R32 heat pumps: the refrigerant alone does not solve the issue of peak loads.

Without an adequate storage system, the heat pump is forced to follow the instantaneous load, often working outside its optimal efficiency point — a topic explored in the article on heat pumps and thermal batteries as a fast answer to traditional storage limitations.

The key point is that HP efficiency depends on integration with storage, not just on the gas choice.

Why there's no need to push HPs beyond 60°C

A well-designed system allows:

• the heat pump to operate at lower, more stable temperatures;
• energy to be stored when the load is low;
• heat to be released quickly when the user demands it.

In this scenario, there’s no need to design the entire system to constantly operate at 60–65°C, even when there is high DHW demand. This applies to the R290 vs R32 comparison as well as to unit sizing.

PCM thermal storage: different from traditional tanks

This is where PCM thermal storage comes into play, particularly the i-TES thermal batteries.

Unlike traditional tanks:

• they do not store large volumes of water;
• they store thermal energy in the form of latent heat;
• they release high power in a short time.

This makes them particularly suitable for heat pumps for domestic hot water heating, because they:

• separate energy production from instantaneous demand;
• reduce peak loads on the HP;
• allow lower production temperatures to be maintained.

Unlike traditional storage, PCM thermal storage doesn't store large volumes of water, but thermal energy — a substantial difference explained in the comparison between traditional electric boilers and i-TES thermal batteries for domestic hot water.

DHW and concentrated demands: a real issue

In many real-world applications — hotels, gyms, hospitality structures, shared housing — the issue is not theoretical, but daily:

• many users requiring DHW at the same time;
• short but intense peaks;
• need for immediate comfort.

In these contexts, discussing only the heat produced by the heat pump or maximum temperature is reductive. An intelligent system management is needed. In facilities with concentrated DHW demand — such as hotels, gyms or collective residences — the issue of immediate hot water availability is not theoretical but real, as shown in the in-depth look at the relationship between heat pumps and thermal comfort in peak demand management.

R290 or R32? Why the system matters more than the refrigerant in residential applications

In the residential market, choosing between R290 vs R32 is not just a matter of performance, but also of costs and space. Propane (R290) heat pumps, while excellent, are often more expensive and bulkier than equivalent R32 versions.

Often, an R290 unit is chosen just to guarantee high-temperature DHW production or for disinfection cycles. However, integrating a PCM thermal storage with a melting temperature below 50–55°C completely changes the game:

• No Legionella risk: Since these systems store thermal energy as latent heat and not stagnant water, there's no need to push the system above 50–60°C for sanitation.
• Efficiency with R32: Operating at lower supply temperatures makes an R32 heat pump — generally more affordable and compact — perfectly suitable for DHW production.
• Space optimization: The higher energy density of PCM allows for a more compact storage system, ideal for residential settings where every square meter counts.

In short, using PCM avoids the need for investing in more complex and expensive R290 units, while ensuring comfort and hygiene with lower operating temperatures and simpler mechanics.

In conclusion: Design the system, not just the unit

The comparison between R290 vs R32 gas cannot be reduced to a simple race for the highest achievable temperature from the unit alone. The real differentiator for an efficient and sustainable system is the design of the system as a whole.

While in commercial settings or extreme retrofit cases R290 remains the go-to choice, in the residential sector, integrating a PCM thermal storage opens up far more advantageous scenarios:

• Cost optimization: Allows the use of R32 heat pumps, generally more compact and affordable, without compromising comfort.
• Efficiency and Safety: By managing DHW peaks via latent heat, there's no need to push the HP to 60°C, effectively eliminating the Legionella issue without energy-intensive thermal cycles.
• Reliability: Reducing mechanical stress on the unit increases its lifespan and reduces maintenance needs.

For designers and energy managers, the smartest solution is not necessarily the most powerful unit, but the one integrated into a system capable of managing energy dynamically. Choosing the heat pump and PCM storage combo means offering a compact, safe, and truly optimized system for the needs of the modern user.